April is spider behavior month*, folks! Are you ready? Are you excited?

YIEuN(*I decided this by myself.)

I know many people aren’t super fond of spiders, and hey, there’s no shame in that. Deep within the heart of many a human is an impulse to get the jitters when we see something small, black, and crawly. I’m even going to discuss some theories for why that is in a moment.

But to simply fear and loathe spiders is to do them a disservice. They are an extraordinarily successful group of arthropods that live on every continent besides Antarctica (so, if you really want to avoid them, go there) and are the seventh most diverse order on the planet, with over 45,000 different species known to man.

In terms of evolution, spiders are a Big Deal. And I guarantee that the more you learn about them, the less frightening they’ll be!

Throughout April I’m going to write three different articles on spider behavior, because yes- there’s too much behavior to fit into just one. Today’s article will pull double-duty as both an introduction to the physical diversity in spiders as well as a more in-depth look of some of their amazing hunting techniques.

But first, before we discuss spider behavior, let’s go off on a little tangent about human behavior. Why are so many people afraid of spiders?

The Psychology of Arachnophobia

Arachnophobia, being a phobia, is rather worse than just a general nervousness around spiders. Those with the phobia may be affected so badly that they have panic attacks even at the mere thought of a spider being in a room. It’s estimated that roughly 5% of the population could be diagnosed with this phobia, which is a huge amount.

But even if your discomfort with spiders isn’t severe enough to be classified as a phobia, spiders seem to make most people just that: uncomfortable. Why is this?

One of the more popular theories is that humans are programmed to be wary of spiders because there are several species with venom potent enough to be deadly to humans. In this case, the fear would be hardwired into our genes for our own safety. However, the number of spider species that actually pose a threat to humans could be counted on your fingers; the vast majority of spiders are completely harmless. It seems rather extreme to have evolved a hardwired anxiety for spiders to combat a few, widely-scattered species. (Especially considering how exaggerated the danger of even these species is, as I expanded on here.)

Skeptics of the evolutionary theory point out that fear of spiders is actually less common outside of Western European societies; consider, for instance, the West African god/mythic figure Anansi, who usually takes the form of a spider. Anansi, while often depicted as a trickster, is also a wise and benevolent fellow who gave humans the gift of agriculture, among other things. In parts of India and Pakistan the spider is actually considered a sign of good fortune, in Egypt there’s a tradition of putting a spider into the bed of a newly-married couple, and in many South American countries spiders often find their way onto the menu. Not what you’d expect to see if humans have a hardwired fear of spiders!

A Native American shell gorget decorated with the image of a spider.

A Native American (likely Cherokee) shell gorget decorated with the image of a spider.

Most completely negative perceptions of spiders, in fact, stem from Western culture, and most start appearing in the Middle Ages. (Even in the Greek story of Arachne, spiders are depicted as skilled weavers and not villains.) In 11th-century southern Italy, reports of a literal dancing fever began to spread: this was of course “tarantism,” attributed to the bite of of Lycosa tarantula, which confusingly enough is a type of wolf spider. It is also completely harmless to humans. However, the medieval Italians believed quite strongly that the bite of this spider caused fever, excitability, vomiting, and sweating, and that the only way to survive was to begin dancing the tarantella until you dropped.

Also prevalent during the Middle Ages was the concept that spiders carried disease, and that any food or water that came in contact with the spider was poisoned. Spiders were even seen as harbingers of the black plague.

Supporting the cultural theory of arachnophobia is the fact that many studies have found that humans tend to associate spiders more strongly with disgust, along with harmless creatures such as slugs and maggots, rather than fear along with creatures such as bees and wasps. There is also no consensus among arachnophobes as to what the most frightening features of spiders are (the legs? the eyes? the fuzziness?), which one would expect if we had a hardwired genetic anxiety.

Despite this compelling evidence for a Western European cultural cause for spider disgust, there has yet to be a cross-cultural study examining attitudes towards spiders to my knowledge. And there is some evidence that humans are predisposed to fear spiders. Arachnophobia tends to run in families, though the predictor is level of disgust rather than fear of spiders. And children as young as three tend to show fearful reactions to spiders.

The answer may actually lie in between a cultural and genetic source for this phobia. Studies with another commonly-feared animal, the snake, have shown that while primates may not be born with a fear of snakes, they learn it much more easily than other fears and take a lot of convincing to give it up. The experiment in question showed several rhesus macaques who had never been exposed to snakes images of snakes and flowers: the monkeys were afraid of neither. Then the researchers paired the images with footage of a monkey reacting fearfully. The macaques immediately picked up the fear of snakes, but not the fear of flowers. So we may pick up fear for animals that are potentially dangerous much more easily thanks to evolution.

A study with humans pairing images of spiders with electric shocks found that the fear of spiders is much harder to extinguish once learned than fear of things such as flowers and houses. (Why flowers again? Also, what a horrifying experiment that must have been.)

Luckily for those of you who are arachnophobic, the phobia is very treatable regardless of the cause. Exposure therapy is often the easiest way to get over it (seeing other people interact calmly with spiders is known to help), though for people with extreme arachnophobia, drugs such as beta blockers and D-cycloserone can also help when used along with therapy. There is actually even an iOS app out now called “Phobia Free” designed to desensitize arachnophobes to spiders.

So, in summary: very few spiders are actually dangerous, fear of them is probably mostly cultural (but may be a type of fear we are predisposed to learn), and the fear, while hard to extinguish, can be extinguished with the right treatment.

All right, that’s enough about human behavior. Let’s get on to the spiders!

Know Your Spiders

Spiders are, as most of us know, arachnids, along with scorpions, psuedoscorpions, whip scorpions, ticks, mites, and harvestmen, among others. Arachnids are most commonly identified by the fact that they have eight legs rather than six as in insects, though not all of them actually have eight legs. The actual feature that all arachnids have in common is the presence of chelicerae and pedipalps, two pairs of appendanges that resemble fangs and a shortened pair of legs, respectively. The chelicerae are used in feeding, while the pedipalps are used like arms.

Different types of chelicerae. A) jacknife, b) scissor, c) three-segmented chelate.

Different types of chelicerae. A) jacknife, b) scissor, c) three-segmented chelate. Spiders have type A.

As I mentioned before, the order of spiders in particular (Araneae) is among the most diverse of any in the animal kingdom, with over 43,678 species recorded to date. The order is divided into three suborders: Mesothelae, Mygalomorphae, and Araneomorphae. Mesothelae is the most basal of the suborders and contains only about 87 species. The most famous of these are the trapdoor spiders- we’ll get to them.

Mygalomorphae is more or less the “big scary spider clade” as it includes both tarantulas and Australian funnel web spiders. Unlike other spider species, which live for about a year, these ones can actually live for up to 25 years! Rad.

The final and largest suborder, however, is Araneomorphae. This clade includes such characters as lampshade spiders, crab spiders, cobweb spiders, jumping spiders, wolf spiders, orb weaver spiders, huntsman spiders… look, there are a lot of spiders out there, and most of them are Araneomorphs.

Spiders as a group first emerged on the scene about 300 million years ago during the Carboniferous period, predating such creatures as mammals and dinosaurs. It was a great time for arthropods in general- the climate was highly moist and oxygenated, and arthropods, which breathe via diffusion, were loving it.

The first spiders were within the Mesothelae suborder, and included species such as Eocteniza silvicola and Protocteniza britannica. These spiders were very small (P. britannica was about 15 mm long), slow-moving, and had their spinnerets located in the center of their abdomen like belly buttons rather than at the end like modern spiders. They were most likely ground-dwellers that built rudimentary nests or trapdoors with their silk.

Ancient spiders probably looked similar to modern Mesothelae spiders, like this Ryuthela secundaria. (Photo source.)

Ancient spiders probably looked similar to modern Mesothelae spiders, like this Ryuthela secundaria.         (Photo source.)

Quick note on some prehistoric not-spiders: Attercopus (Tolkien fans, recognize the name?) was once believed to be the earliest genus of spiders, as they lived during the Devonian era 380 million years ago, but has since been reclassified as belonging to a sister taxon. The chunky Megarachne servini, which lived 298 million years ago, was once thought to be the largest spider ever: 20 inches long from end to end. This was even promoted in an episode of the documentary series Walking With Beasts. However, the fossil used for the classification was actually that of a sea scorpion! The foot-long goliath birdeater tarantula retains its title as the largest spider ever, and happily for us it is still alive today.

And she's beautiful! (Photo source.)

And she’s beautiful! (Photo source.)

Ok, anyhow: by the Triassic, Mygalomorphae and Araneoporphae showed up, and it was basically spider time, all the time from there.

My favorite time of day!

My favorite time of day!

 What Spiders Do

Ok, this has been a really long introduction to spider behavior month without any actual spider behavior. So let us get down to brass tacks, as they say. Spider tacks.

Most species of spider are strict carnivores that mostly prey on insects and other small arthropods. Some do prey on larger beasts such as mice, lizards, and birds, though accounts of this are often exaggerated. Spiders evolved in tandem with their prey insects and are best equipped to deal with things that have an exoskeleton.

Spiders possess specialized chelicerae that are pointed and hollow for injecting venom into their prey, which immobilizes it for pre-digestion. This is because spiders evolved to have a totally liquid diet. This enables them to minimize the size of their digestive tract and maximize their ability to store food for long periods of time, which is useful if your main hunting tactic is hoping an insect will bumble into your web. I went into the digestion of spiders in a lot more detail here, by the way, and even discussed whether or not they can fart. (They theoretically could.)

There is at least one species of spider that feeds almost exclusively on plant matter: the recently-discovered Bagheera kiplingi. The vast majority of their diet consists of Beltian bodies, which are basically little nutrient-rich nubs that plants put out to attract ants. The ants then protect the plant. Ironically, B. kiplingi does no such thing in exchange for the meal, and the ants and it do not get along. Upon occasion this spider does eat meat, though this mostly consists of snatching ant larvae or others of its own species.

B. kiplingi is a pretty handsome spider, all things considered. (Photo source.)

B. kiplingi is a pretty handsome spider, all things considered. (Photo source.)

B. kiplingi is not the only species known to be omnivorous, though: many spiders will partake in nectar, fruit, or pollen upon occasion, particularly juveniles who’ve still got some growing to do.

What about spider speed and strength? Well, spiders are not the cheetahs of the arthropods; they have primitive respiratory systems and prefer to ambush prey rather than chase it down. They draw in air through their spiracles, which are located on their rear abdomen close to their spinnerets. So yes, spiders do breathe through their butts.

Being poor respirators is why spiders do that little “jerk and move a few steps away” thing when you poke them. They don’t want to waste energy by running further. And if you poke them enough, they may perform the “catapult myself into space” escape strategy, which can, unfortunately, land them on your face. So please let the poor things be.

An interesting tidbit on spider locomotion: while spiders use muscles to retract their legs, they use hydraulics to extend them. That’s right: the inside of a spider is pressurized. This means that if you were to puncture their cephalothorax, they essentially “pop.” Aside from the likelihood of spider stuff squirting out, the loss of pressure means that the spider will be unable to extend its legs. This is also why the legs of dead spiders curl up.

Here's a little spider anatomy for ya.

Here’s a little spider anatomy for ya. Blue = nervous system, red = circulatory system, yellow = digestive system, and purple and green are reproductive organs and silk production, respectively. Click to enlarge. (Photo source.)

All spiders have four pairs of eyes, and the vision of certain species is among the best within Arthropoda. Their two main eyes, located at the front of the head, are capable of forming images, while their secondary eyes (usually located at the sides and/or top of the head) expand their field of vision and have varying degrees of complexity. They also come in lots of different spatial arrangements depending on the spider’s hunting preferences. Web-spinners and lurkers like crab spiders tend to have small eyes clustered all together at the front of their face, while more active hunters have large eyes circling their head.

Several spider eye arrangements. Clockwise from top: jumping spider (), orb weaver (), unidentified, and wolf spider (). (Photo sources: 1/2/3/4)

Several spider eye arrangements. Clockwise from top: jumping spider (Clynotis severus), orb weaver (Eriophora transmarina), wolf spider (Hogna sp.), and an unidentified species. (Photo sources: 1/2/3/4)

If you ever go out late at night during the spring with a headlamp on, you will see lots of tiny glittery things down in the grass. These are the reflections from the eyes of nocturnal spiders that have tapetum lucidum, much like cats do.

Sight is not the primary sense of the web spinner, as evidenced by their tiny lil’ eyes. Instead, they depend on sensitive hairs and bristles known as setae, which can do basically anything: They can touch! Detect vibrations! Smell! Taste! Sense changes in the air pressure! This means that a spider walking over your face is essentially smelling and licking you. Suddenly, all your spider encounters just got a whole lot more intimate.

Aside from their eight legs, spiders also have pedipalps, which resemble a shortened pair of legs covered in setae right by the face. While they look like legs, they are probably actually modified antennae from an arthropod ancestor. Spiders use these palps like little hands, rotating and examining food, cleaning their faces, and for males, even transferring sperm to the female during mating. (We’ll get to the harrowing experience of spider sex in a later post.)

A male striped lynx spider and his big fluffy pedipalps.

A male striped lynx spider and his big fluffy pedipalps. It’s for the ladies.

Here is a rather enchanting video of a jumping spider wiggling its palps and cleaning itself.

But aside from all that other anatomy (cute as it may be), the part of the spider I am most fascinated by is the brain. Yes, spiders have brains, and pretty large ones too by arthropod standards. Also unlike other arthropods, their ganglion are centralized in their cephalothorax and not spread throughout their body. The interior of the cephalothorax is actually mostly composed of nervous tissue, pushing some organs like coxae down into the legs.

Jumping spiders (Salticidae) are acknowledged as some of the brainiest of spiders. In some experiments, jumping spiders were able to learn and remember color cues in order to locate a food item. Recently, some scientists even managed to insert a really tiny electrode into a jumping spider brain and found that the spider used single neurons to do tasks (combining information from eight different eyes) that would take vertebrates many more.

The real intelligence of spiders is in their hunting strategies, however, and some spiders use surprisingly clever tactics. But let’s begin with the web-spinners.

Silky Killers

Which came first, the spider or the silk? Well, the silk, actually. I mentioned Attercopus earlier as an arachnid once thought to be a Devonian-era spider; this was thought because Attercopus possessed spinnerets. So the ancestors of spiders made silk before they were spiders.

The earliest known spider web was found fossilized in amber from 100 million years ago- this leaves a gap of 200 million years from initial spider origins. So what were spiders doing with their silk all that time?

Well, silk has many, many uses aside from web-spinning. In fact, spinning webs is only a fraction of what modern spiders use their silk for- of those that even make webs! Spiders use their silk for things such as protecting their eggs, climbing vertical surfaces, and even mating.

The earliest spiders probably hunted in similar ways to modern trapdoor spiders: they dug a burrow, lined it with silk to keep it clean and dry, and constructed a trapdoor with dirt and detritus that they could affix to their hole with a silk hinge. Then they sat, and they waited.

The speed of the strike comes from the fact that the spider rests its legs on slender lines of silk it placed all around the burrow. As soon as one twitches, the spider lunges with rather alarming speed and accuracy.

From these early home-hunters rose spiders that used their silk in increasingly complex ways. The earliest webs were probably sheet webs, basic sticky silk covering a small plant or landmark on the ground to catch crawling insects. Later innovations included funnel webs, tubular webs, tangle webs, and finally the famous spiral orb web.

The five basic spider web types. Top left: sheet web. Top right: spiral orb web. Center: tangle web or cobweb. Bottom left: funnel web. Bottom right: tubular web.

The five basic spider web types. Top left: sheet web. Top right: spiral orb web. Center: tangle web or cobweb. Bottom left: funnel web. Bottom right: tubular web. (Photo sources: 1/2/3/4/5)

Of course, that is about as generalized overview of web types as you can get. The variations are endless, and the evidence suggest that many lines of spiders have lost the ability to spin webs and then regained them several times.

Spinning silk isn’t one-size-fits-all, either. While some spiders can only produce one or two types of silk, some species can produce up to eight different types for different purposes. Here are just a few examples:

  • Tubiliform: a stiff, non-sticky silk used for protecting eggs
  • Apullae (major and minor): Ampullae major is a strong, non-sticky silk used for securing draglines. Ampullae minor is used as stand-in scaffolding during web construction (and is eaten when the gaps are filled by other silk types).
  • Pyriform: a strong, sticky silk used for gluing different lines together.
  • Flagelliform: stretchy and sticky. Used in the capture spiral of orb webs.
  • Aciniform: the toughest silk of all, used for wrapping up prey. Also used to gift-wrap spider sperm.
  • Aggregate: lines with large sticky droplets, used by bolas spiders.

Producing silk has a high energy cost, so many spiders will take care to eat any excess when repairing or rebuilding their webs. Some spiders actually steal web material from other spiders to eat.

The sit, wait, and wrap-it-up method of prey capture used by web-spinning spiders is hardly the only one, though it is certainly the most familiar one.

But many spiders use their webs in a much more… active way. Take the net-casting spider: it does exactly what its name implies.

VpVpo37By the way, uhh… take a look at the eyes on this fellow.

Does this make you uncomfortable?

Does this make you uncomfortable?

I also mentioned the bolas spiders earlier, and they too hunt exactly as you would expect.

To finish up our trio of spiders-that-do-exactly-what-their-name-implies, there are the spitting spider. Unlucky prey will encounter a faceful of silk imbibed with paralyzing venom. I didn’t include a video of this one because the action happens so fast that it looks like the prey item just stops moving on its own.

But of course, there are other even weirder ways to use webs. My favorite is the diving bell spider. As previously mentioned, spiders breathe through their butts. The diving bell spider traps air using the hairs around its abdomen and proceeds to hunt prey underwater like an eight legged scuba diver. You thought you were safe in the water, bugs??

Not only does the diving bell spider trap air for use when hunting, it builds large air bubbles underwater, which it anchors with silk. In these pockets it can eat prey at its leisure without running the risk of getting snatched by any landlocked predators.

Now, as cool as all these web-spinning and prey-catching techniques are, they are not based on intelligence. The spiders have the behavior encoded into their genomes and never have to learn it. But there is one group of spiders that do learn their hunting techniques, and use them to outwit their insect prey. I am talking, of course, about the jumping spiders of the genus Portia.

Portia Power

Aside from a line to help secure themselves during their jumps, most jumping spiders do not use silk to aid in their hunting. Instead, they stalk, chase, and lunge at their prey like tiny springy lions. Within Portia, however, members do spin webs to catch small insects- though they still stalk their preferred prey: other spiders.

P. fimbriata. The spider's anatomy is meant to mimic a piece of detritus caught in a web. (Photo source.)

P. fimbriata. The spider’s anatomy is meant to mimic a piece of detritus caught in a web. (Photo source.)

But how do you trap a spider that is already trying to trap other creatures (and potentially, you)? The answer is carefully and cleverly. Portia spiders will find their way to the edges of the webs of their prey and delicately pluck, drum, massage, wiggle, and even slap parts of the web. The web owner, fooled into thinking there is a delicious morsel waiting for it, runs right into Portia’s jaws.

Sounds simple enough- but it really isn’t. There are a myriad of different web-spinning species that Portia might prey on, and they each have their own rhythm. If the vibrations don’t sound just right, Portia might not encounter an unsuspecting victim but an enraged homeowner. This can be dangerous- many of Portia’s prey items are much larger than it is!

Good vibrations aren’t the only thing Portia spiders have to memorize. They also stalk several different spider species, including other jumping spiders. To attack from the front or the rear, which behavior patterns to look out for, and many other tricks must be stored in Portia’s repertoire. How does the little spider manage it?

Well, some of it is based on instinct. Portia occasionally prey on spitting spiders, which I mentioned before- they’re the faceful-of-silk-and-venom guys, and they’re about as pleasant as you’d expect. To complicate things, they also like to eat other spiders- so it can get into a real spider-eat-spider situation. Portia, even those that have never encountered a spitting spider, prefer to attack them from behind to avoid the whole… you know. So this seems to be a genetically encoded behavior.

But other behaviors are not. After all, other spiders don’t always react in exactly the same way: many are able to learn from experience themselves, at least when it comes to interpreting the vibrations in their webs. In these cases, Portia have to mix it up. They may alter the signals they send out through their prey’s webs using trial-and-error to figure out what elicits the best response. For example: a rapid approach might be fine for a small prey spider, and Portia can mimic a small, rapidly-struggling insect. But if the prey in question is larger than Portia, this is not a good idea. For these spiders, it might be better to imitate something very large, or just send confusing signals, so that the prey item approaches more slowly. They can manipulate the speed, predatory behavior, and even the angle of approach from these spiders through their vigorous drumming.

A major sign of intelligence is flexibility in behavior, and Portia have it in spades: when their pre-programmed methods fail, they switch over to trial-and-error, and learn what words and what doesn’t. They may even be able to plan ahead! In one experiment, Portia were placed in a maze where they could clearly see but not reach a prey item in front of them. The spiders quickly learned to take a detour even if it meant that the item went out of sight for a while. This may not sound that smart, but it’s a task many vertebrates will fail.

The brain of a Portia spider is about the size of a poppy seed. (Portia spiders are about the size of a thumbnail themselves.) Compared to vertebrate brains, the number of neurons it possesses are minimal. The drawback to this is that these spiders often have rather slow processing speeds, especially for visual criteria. But can you blame them? They’re using single neurons for tasks that would take humans twenty!

Wrapping Up The Spiders

I hope you lot enjoyed this very long, very generalized introduction to the world of spiders and their behavior. They are fascinating, diverse creatures and I would have to write several books to truly do them justice. But since I don’t have time for that right now, I hope even you spider experts out there learned something from this article!

But don’t fret. In a week or two, I’ll be posting the second of the three-article series on spider behavior. I hope you guys enjoy reading the word “stridulations,” because it’s all about hot, sticky spider sex.

The next spider article is up- read about erotic spider activity here! Or, if you’d prefer to take a break from the sticky fellows, you can read about other things like why animals play and bird yaoi here on my site. (Full list of articles here!)


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The Casual Murders: When Do Animal Lives Matter?

*Note: this essay, obviously, discusses animal death. Sensitive viewers are advised to be cautious.

During my college years, I worked for an environmental consulting company for a summer that was mist-netting for bats. If you have never mist-netted for bats (or birds), well, it can be quite a treat. Technicians set up delicate, nearly-invisible nets within gaps in the canopy to catch flying creatures unawares. The purpose of this is to be able to quickly identify and survey what is flying in the area in order to study them; the animals, sparing any accidents, are then released unharmed.

One of the unwilling subjects of our study.

One of the unwilling subjects of our study.

Since we were mist-netting for bats, we had to set up our nets at night, of course, and our nets occasionally caught other flying nocturnal creatures besides bats. We caught flying squirrels on occasion (don’t let their cute looks fool you, they bite far harder than any bat) as well as catbirds and even small owls. But the most frequent unwanted guests in our nets were giant nocturnal moths.

There was the occasional giant, gorgeous luna moth, but more common were brown polyphemus moths and yellow imperial moths. Both of those species are still quite striking and have a wingspan than can surpass the length of my palm, so I have to admit that I was enchanted when I first saw them. And when they got caught in our nets, I wanted to free and release them.


A polyphemous moth.

This was not what most of the biologists and technicians mist-netting for bats did, and a few scoffed at my attempts to rescue the insects. The problem is that it is much harder to detangle a soft-bodied insect from a fine net than it is to detangle a vertebrate with flesh propped up by firm bones. Removing the moths from the nets was time-consuming and inevitably they would come away wounded at best, with many scales missing from their glorious wings due to incessant flapping.

An imperial moth caught in one of our nets.

An imperial moth caught in one of our nets.

My enchantment with the giant moths waned rapidly as I spent more time mist-netting. Their struggles alerted the bats to our nets, driving them away, and on some nights our nets would simply be full of bright flapping wings. And they tended to reward their rescuers by slamming straight into their faces.

I regret to say that I only spent a few nights freeing moths. After a while, I began doing what the more experienced techs and biologists did: I ripped them out in pieces.

It does not sound pleasant, and it was not: I still remember the dreadful popping sounds. And the first time I did it, I was actually sickened by myself, watching the halves of the moth that I had destroyed flap vainly on the ground in the throes of death.


One of my final rescues pictured here.

But that was the first time. As it got later in the season, and we grew busier and busier- netting twenty, thirty, forty bats each night- the removal of moths became methodical.

I bring up this anecdote because it is a good example of animal death becoming casual. Moths are indeed animals, and very attractive ones at that. To have killed so many of them at a point in my life feels very disturbing. I certainly would attempt to free, rather than crush, a moth that I found caught in something now. Why the change? Because I find them less annoying when they aren’t interfering with my work? But isn’t a life a life, no matter the circumstance?

But here’s another wrinkle to this tale. That same summer, I killed hundreds of mosquitoes without a second thought. Both moths and mosquitoes are insects: but only killing the moths feels bad, because they are attractive to my human eyes.

Our perception of death, I think, changes constantly. As I mentioned before, we obviously want to believe that a life is a life no matter what. Yet it is difficult- I would argue impossible- to follow through with this credence. So if all lives aren’t equal, which lives do matter? Most restrict it to animals, ignoring plants, fungi, protists, archaebacteria, and bacteria- even though all those groups combined make up the vast majority of life, of which animals contribute just the tiniest sliver. We believe that animals have more of a right to live even than plants; this is obviously due to our own bias and perceptions.

A series of deer vertebrae I found embedded in the ground.

A series of deer vertebrae I found embedded in the ground.

But fine, let’s limit it to animals. We still give some animals more allowances than others. Moths deserve to live more than mosquitoes because they are more attractive and usually don’t bite us. Vertebrates deserve to live more than invertebrates (with the exception of the charming octopuses and other cephalopods) because they look and act more like us. Furry vertebrates get precedence over reptiles, fish, and amphibians… and so on.

At this point you could bring up the fact that some animals have a greater capacity to suffer than others. A bear, for example, is capable of feeling more complex pain than, say, an earthworm.

A luna moth, battered from an encounter with one of our nets.

A luna moth, battered from an encounter with one of our nets.

This is difficult to flawlessly prove, but probably true. But the thing is that we are not talking about suffering: we are talking about death. There are different shades of suffering; there is only one kind of death, and everybody, from single-celled protist to hairless ape, experiences it the same way.*

So while we can argue a great deal about suffering and the proper contexts that animals and others deserve to live their lives in, death is separate from all that. Death can result from suffering, it’s true. But it’s also true that we often euthanize our pets to stop their suffering.

As Gavroche said in Les Misérables, “Everyone’s equal when they’re dead.” So, again: if a mosquito and a chimpanzee experience death in the same way, is it really right to value one life over the other?

From a biologist’s point of view, yes. It is a factor of numbers: the mosquito population can survive the losses of thousands upon thousands of individuals each summer, but not so the ape population. But in this scenario, based upon populations, the right to life of any individual is totally erased: all that matters is how many there are in total. This would be terrifying if, say, we ever applied it to human populations (and in fact, across history, we have).

A pair of mating imperial moths.

A pair of mating imperial moths.

I’m not in favor of advocating for any lethal human-population control measures myself. Of course I’m not, I’m human too! And I think most humans would agree with this. But the problem is if we then try to apply this same rhetoric to the lives of other animals: simply put, we usually can’t follow through.

I think we all have to admit that we are biased.

And I don’t think that our bias is necessarily a terrible thing.

One of my early rescues rests momentarily on my face.

One of my early rescues rests momentarily on my face.

I don’t know whether valuing the life of an individual mosquito over the life of an individual human is really right or wrong. Right and wrong are quite frequently hard to discern; especially when you realize that there really isn’t a user’s manual on morality. But should we feel ashamed if we value human life over animal life? No, I don’t think so. I think it’s a factor of self-preservation; it’s who we are. And we value the lives of animals that look, act, or think like us more than those that do not because of this sense of self-preservation. Because if we apply death to these individuals, it feels only a step away from applying death to ourselves.

It stems from the most primitive type of morality: empathy. But our empathy is rarely fixed firmly in one place. When I was busy and the moths got more annoying, I killed them; otherwise, I did not. My sense of empathy was totally dependent on the circumstances, and it’s a little terrifying to realize.

When is a death a casual death? When is death excessive, and when is death acceptable?

We all need to admit that the answers to these questions are constantly changing. And I hope you didn’t read through this essay expecting me to give them definite answers: I cannot. If you think you can do it, kudos to you.

Perhaps, though, rather than considering the cost of death to the dying animal, we should focus more on what that death gives to the survivors. A mosquito, as far as we know, will not mourn for one of its smashed brethren: but the loss of a matriarch will shatter an elephant herd. Conversely, the deaths of a few hundred overpopulated deer might alleviate the suffering of their starving, disease-ridden brethren.

Yet this is not still not flawless, because we can’t apply it to humans. We still have to be biased: I think it is wrong to say that a human with no family deserves to live less than a human that would have a hundred mourners at her funeral.

Maybe the final difference there is that we are the only animals who have a concept of death, and are able to stay awake at night afraid of it.**

But who really knows? Again, I don’t claim to have any answers, though I think the most probable one is our inherent need for self-preservation. And honestly: is it wrong?

I am sorry about the moths I killed, though.

A caterpillar, species unknown, dropped from a silken line onto my knee. I set it down in the grass.

A caterpillar, species unknown, dropped onto my knee. I let it crawl away unharmed.



*Ok, not totally. Sometimes it is hard to define death when, say, an individual has their heart transplanted; similarly, organisms can swap cells and pieces of themselves all the time and how do you even define life, for that matter?? Is it just DNA? Are viruses alive?
**It’s interesting that I wrote this article with such a firm concept for what death is, yet now I can’t even come up with a proper definition of it. Well, I’ll see myself out.

Kleptoparasitism: Defense Against The Big Bullies

Note: some of the videos embedded in this article show predators eating animal carcasses.

To describe what kleptoparasitism is, I’m going to use a Pixar film.

I don't remember this poster looking so ominous.

I don’t remember this poster looking so ominous.

Yes, Pixar’s 1998 film A Bug’s Life, while incorrectly making worker ant Flik a male*, provides a very excellent example of kleptoparasitsm. Poor Flik’s ant colony is forced to gather extra food every year in order to offset the losses from the larger and more aggressive grasshoppers, who regularly come and steal the ants’ food.

While real grasshoppers aren’t known for pilfering from ant food stores (they would find themselves very quickly dismembered and tossed on the pile), this type of interaction is very common between types of species that share the same food source, or need the same types of resources, such as nest-building material. Generally, it is the larger, more powerful species that nabs the resource from the smaller one. Hence the term ‘kleptoparasitism’: parasitic theft.

Most kleptoparasitism takes place opportunistically- few species have evolved to be thieves one hundred percent of the time because it’s simply not practical. The only exceptions to this occur if you consider brood parasitism a kind of kleptoparasitism. For example, common cuckoos exclusively make use of the nests built by other birds and have lost the ability to care for their own young. Conversely, slave-making ant species actually steal the young of other ants to do all the work in their colony. Et tu, Flik?

Kleptoparasitisitic relationships can also occur between members of the same species- one could consider the nabbing of prime territory or mates a form of kleptoparasitism. In fact, many species that have kleptoparasitic relationships with one another are very closely related, particularly in insects. This makes sense- the more similar you are, the more you compete for the same resources.

The relationships I want to talk about the most today, however, are the ones between species that are not closely related, but share the same ecological niches. And I want to discuss an interesting hypothesis, one that was also explored in A Bug’s Life. If you’ve seen the film, you’ll remember the ending:

Yep, Flik saves the day and helps his colony defeat the grasshoppers by reminding them that they vastly outnumber their parasites and, additionally, are equipped with limb-severing pincers. The ants are then able to overwhelm the grasshoppers with sheer numbers and presumably feast upon their remains offscreen.

So: how effective are numbers as a defense against kleptoparasitism?

Kleptoparasitic Relationships Between Large African Predators

Kleptoparasitism is a major problem for mammal species of a particular kind: small, lightweight, and specialized predators. On the African savannah, two species are notable targets for kleptoparasitism: the cheetah and the African wild dog.

Of the large mammalian predators on the savannah- the lion, leopard, cheetah, hyena, and wild dog- it is the cheetah and the dog who have the highest hunting success rates, of about 50 and 80 percent, respectively. Comparatively, hyenas and lions have closer to 30% success rates when they attempt to make a kill.**

Hyenas and lions, while not as speedy or efficient as the dogs and cheetahs, certainly know how to use their greater weight to their advantage- hyenas weigh about twice as much as both species, while lions have nearly four times their bulk. It is estimated that about 50% of all cheetah kills are parasitized by lions or hyenas, a rather grim statistic for an endangered species.

Unfortunately, there is very little a single cheetah can do against a hyena. Aside from the differences in weight and power, the specialized hunting style of the cheetah means that any injury could be fatal. Cheetahs (and wild dogs) are cursorial hunters, which means that they chase their prey over long distances. This requires a lightweight body and excellent stamina. A lion might be able to stalk and ambush its prey with minor injuries, and even with major ones it still has a chance of using its weight to steal prey from smaller creatures. But cheetahs and wild dogs hunt nearly exclusively for their own food.

The lion is the heaviest predator on the savannah, and they know it: as many as half of the kills a lion eats might be stolen from other predators. They kleptoparasitize even more than the much-maligned hyena, which in some studies hunts for as much as 95% of its own food.

However, hyenas can also kleptoparasitize the larger and more powerful lions. Their secret? Just as with the ants, it lies in numbers. If a group of hyenas outnumbers the lions feeding at a kill by a factor of four, they may challenge them. It’s a toss-up to whether or not they will succeed, though the presence of much larger male lions can make things much more dangerous. One study found that 71% of all hyena mortality was due to lions.

In fact, lions are a major cause of death for all of their competitors. African wild dogs and cheetahs also have much to fear from lions: lions will seek out and kill their cubs without even bothering to eat them afterwards. For this reason, while these species can forge a rough coexistence with hyenas, they actively avoid spaces that lions frequent.

You’ve been lied to, folks: Lions ain’t majestic beasts with flowing hair. Lions are gigantic assholes that make up for their crappy hunting skills by stealing meat from smaller animals. You say lion king, I say lion tyrant.

Remember, son, hyenas are inherently evil and there's nothing wrong with stealing their food and murdering their young. Now go eat your rotting carcass.

Remember, son, hyenas are inherently evil and there’s nothing wrong with stealing their food and murdering their young. Now go eat your rotting carcass.

So on the savannah, killing your prey may be the simple part: the harder part is keeping it. Leopards, at least, have solved this issue by dragging their prey up into trees to eat at their leisure, though this doesn’t always work. Other species with less of an inclination for tree-climbing will make their kills in tall grass or dense foliage to avoid detection, though inevitably small scavengers like jackals and vultures will give them away. In fact, at times the scavengers can oust the killers themselves.

Much of the behavior of these smaller hunters, in fact, is heavily influenced by kleptoparasitism- more than you might think. After all, evolution doesn’t work in a vacuum, and if there’s someone out there making it, there’s always someone else ready to try and steal that success.

This raises a rather interesting question: are some of our assumptions about the social nature of these hunters wrong? Recall that if they greatly outnumber lions, hyenas can steal their kills. Conversely, this means that even the lions need to be in large groups to resist losing their spoils. Do these predators group up specifically to reduce kleptoparasitism?

But wait, I hear you say. The reason why animals hunt in groups hunt in groups is because they need to work together as a team to kill much larger animals!

Well… yes and no. Animals that hunt together in groups are actually restricted to larger prey***, because they need to have enough food to feed everybody when they’re done. What feeds six lions more effectively: one impala or one Cape buffalo?

The buffalo looks like it'd eat a few impala itself on an off day. (Photo by Haplochromis.)

This buffalo looks like it’d eat a few impala itself on an off day. (Photo source.)

If you think about it this way, hunting larger prey is a handicap and not at all an advantage- especially when you consider the increased danger from things such as injuries. That cute little impala isn’t going to kick your head in with the same force that a Cape buffalo will. (Also, the impala is less likely to turn around and stomp on your remains to be sure the job is done.)

It’s a fact that most predatory animals- estimates range from 85-90%- hunt by themselves. So what led some animals to seek out big, dangerous prey that they couldn’t finish alone? Probably not the thrill of it all. Remember how dangerous injuries are for some predators? There has to be a big payoff for all that risk.

But perhaps we’re looking at it the wrong way- maybe the tendency to group up evolved before predators started attacking oversized prey. In that case, why did the hunters start working together?

Resource distribution may be a large factor: if prey animals are spread out evenly through the environment, predators will probably have the most success hunting alone. But if prey animals are clumped all together and tend to try to defend one another, a group may have a better chance of splitting somebody away from the herd than a solo hunter.

However, the distribution of resources doesn’t neatly tie up every loose end. While some species have a higher likelihood of making a kill in larger groups, many do not. In fact, most mammalian predators are quite capable of hunting smaller prey by themselves- single wild dogs can kill impala, and it is actually more common for hyenas to kill prey alone than when in a group. In a large study of species that either hunted in groups or alone, ecologists Packer and Rutton actually found that there tended to be no overall benefit in terms of hunting success when animals hunted in groups.

Additionally, most group hunters live in larger groups than the ones they hunt in- hunting parties tend to be cliques that split away from the main group. And the phrase ‘group hunting’ itself may be misleading. While African wild dogs statistically have increased hunting success in larger groups, individual dogs within a hunting party may all initially be pursuing different prey animals at first, then converge upon the first animal that becomes vulnerable. In this sense, they are hunting “alone” until the final moments.

I mentioned earlier that hyenas usually make their kills by themselves: however, they may be trailed by other members of their clan that attempt to take the meat for themselves once the hard work is done. So not only do group-living animals have to share their meat, they might have to share it with individuals that didn’t even help get it. How’s that for a raw deal!

Like, literally raw.

Like, literally raw. (Photo by Marcel Oosterwijk.)

So exactly what advantages do hunting in groups confer? Resistance to kleptoparasitism may actually be a big factor. A hyena may be able to steal from a lone wild dog. But what about ten?

(They may not be able to kill the hyena, but they sure can annoy the shit out of her.)

In this video, finally, the smaller hunters are able to drive off the larger ones and finish their meal. Just like Disney taught us in A Bug’s Life!

Now, I’m not going to suggest that this resistance to kleptoparasitism is the only reason some predators hunt in groups- there’s a whole host of other factors that I haven’t even touched on, like the ones that have nothing to do with eating- group living confers other benefits, especially for a little fellow who might become prey as easily as predator. But I do challenge you to reconsider what you thought you knew about why animals hunt in groups.

Let me close with cheetahs, since I discussed them a great deal earlier. Most cheetahs hunt alone. However, many male cheetahs hunt in groups of 2-3 related individuals known as ‘coalitions,’ some females hunt with their cubs, and some adolescents of either sex will hunt together.

Most studies of cheetahs conclude that while coalitions enable cheetahs to seek out larger prey, the amount each animal eats is no higher than it would if it hunted alone (and may even be less). Resistance to kleptoparasitism may provide benefits- though, surprisingly, one hyena is still capable of scaring three fully grown male cheetahs off a kill.

The answer this time, in fact, probably lies with social behavior and has nothing to do with hunting at all. Female cheetahs tend not to be territorial, and live in vast home ranges overlapping those of many other females. This makes it more difficult for male cheetahs to defend access to females- unless they have wingmen to back them up.

So in the end, cheetahs still kinda get screwed no matter what. Good luck, guys.

No wonder they're always crying. (Photo by)

No wonder they’re always crying. (Photo by William Warby.)


Read on: What about prey animals? Why do they form groups? Shatter your dreams learning why here (hint: lions aren’t the only assholes). If you want to learn about obligate brood parasitism, read about the lives of cuckoos and cowbirds here! And if you want to learn ab0ut an animal that kills its young for shits, try Coot Parenting Tips.

Or just return to the Nonfiction section to see a list of all articles I’ve written. Thanks for reading!


Cangialosi, K. R. (1990). Social spider defense against kleptoparasitism. Behavioral Ecology and Sociobiology, 27(1), 49-54.

Carbone, C., Du Toit, J. T., & Gordon, I. J. (1997). Feeding success in African wild dogs: does kleptoparasitism by spotted hyenas influence hunting group size?. Journal of animal Ecology, 318-326.

Carbone, C., Frame, L., Frame, G., Malcolm, J., Fanshawe, J., FitzGibbon, C., … & Du Toit, J. T. (2005). Feeding success of African wild dogs (Lycaon pictus) in the Serengeti: the effects of group size and kleptoparasitism. Journal of Zoology, 266(02), 153-161.

Caro, T. M. (1994). Cheetahs of the Serengeti Plains: group living in an asocial species. University of Chicago Press.

Cooper, S. M. (1991). Optimal hunting group size: the need for lions to defend their kills against loss to spotted hyaenas. African Journal of Ecology, 29(2), 130-136.

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Creel, S. and N.M. Creel (1995). Communal hunting and pack size in African wild dogs, Lycaon pictus. Animal Behavior 50: 1325-1339.

Durant, S. M. (2000). Living with the enemy: avoidance of hyenas and lions by cheetahs in the Serengeti. Behavioral Ecology, 11(6), 624-632.

Hayward, M. W., Hofmeyr, M., O’brien, J., & Kerley, G. I. H. (2006). Prey preferences of the cheetah (Acinonyx jubatus)(Felidae: Carnivora): morphological limitations or the need to capture rapidly consumable prey before kleptoparasites arrive?. Journal of Zoology, 270(4), 615-627.

Höner, O. P., Wachter, B., East, M. L., & Hofer, H. (2002). The response of spotted hyaenas to long‐term changes in prey populations: functional response and interspecific kleptoparasitism. Journal of Animal Ecology, 71(2), 236-246.

MacDonald, D. (1983). The ecology of carnivore social behavior. Nature 301: 379-384.

Packer, C., & Caro, T. M. (1997). Foraging costs in social carnivores. Animal Behaviour, 54(5), 1317-1318.

Packer, C. and L. Ruttan (1988). The evolution of cooperative hunting. The American Naturalist 132: 159-198.

Packer, C., Scheel D., and A.E. Pusey (1990). Why lions form groups: Food is not enough. The American Naturalist 136: 1-19.

Rostro-García, S., Kamler, J. F., & Hunter, L. T. (2015). To Kill, Stay or Flee: The Effects of Lions and Landscape Factors on Habitat and Kill Site Selection of Cheetahs in South Africa. PloS one, 10(2), e0117743.

Trinkel, M., & Kastberger, G. (2005). Competitive interactions between spotted hyenas and lions in the Etosha National Park, Namibia. african Journal of Ecology, 43(3), 220-224.

van der Meer, E., Moyo, M., Rasmussen, G. S., & Fritz, H. (2011). An empirical and experimental test of risk and costs of kleptoparasitism for African wild dogs (Lycaon pictus) inside and outside a protected area. Behavioral Ecology, arr079.

Watts, D.P. and J.C. Mitani (2002). Hunting behavior of chimpanzees at Ngogo, Kibale National Park, Uganda. International Journal of Primatology 23: 1-28.

*No, I will never get over this.

**Note that these percentages are extremely rough, and vary tremendously based on factors such as group composition, environment, and the experience of the animals involved.

***There are some circumstances where this does not hold true. Chimpanzees, for instance, hunt small prey in groups so that each hunter hopefully catches his own prey, and dolphins and other group-hunting marine predators usually hunt schools of smaller fish.

The Frivolous Function of Play

My good friend Chloe is a mutt without an off button. 8 am? Time to play. 12 pm? Time to play. 7 pm? Time to play. 4 am? Guess what time it is!

Of course such behavior is a pure delight to watch, but as scientists we must ask ourselves the question: why? Why so much play, Chloe? What’s the point?

We appear to have lost Chloe's attention.

We appear to have lost Chloe’s attention.

It may seem silly to ask why play behavior occurs, because after all it’s play. Play! Play is all about fun; what’s there to study? And in fact, that attitude led to play being neglected as a study topic for much of scientific history. But play behavior is a category of behavior just like foraging behavior or sexual behavior or social behavior. If it occurs a lot- and it does- it must be evolutionarily important.

Okay, so we want to study play. So what counts as play behavior?

Seriously, how the hell do you define play?

Continue reading

Bat Flight Versus Bird Flight

Bats are better at flying than birds are.

I can hear all you bird fanatics out there revving your engines, but that’s not just my personal opinion (ok, it mostly is). Still, there are some sound scientific facts in there.

Look, if you compare the effortless soaring of something like a turkey vulture to the frenetic flapping of a little brown bat, of course the bird is going to seem better off. But most people haven’t spent a lot of time around bats, or watching bats fly. Because they generally fly at night.

I spent a summer mist-netting for bats in rural Ohio once, and let me tell you, your opinion on bat flight prowess changes after you have seen a bat fly within a few centimeters of a vertical wall of net and completely reverse direction in midair. All in a split second.

Bats are really, really good at flying.

We still managed to catch some because, as my superior put it, "They get lazy about echolocating sometimes." I suppose I'd get tired of having to scream in order to see too.

But we still managed to net some because, according to my supervisor, “they get lazy with their sonar.” (The bats were not harmed, just irritated.)

There have been only four major groups of animals that have achieved liftoff, and they all achieved it quite differently. The first is the insects, of course, which are among some of the most successful and diverse fliers out there- from dragonflies to butterflies to actual flies. The remainder are among the vertebrates: the pterosaurs, the birds, and of course, the bats. (Arguably, humans too, if you count building flying metal thingies.)

All other “flying” animals you may have heard of, such as flying squirrels, are actually gliders.

We caught THEM in our nets as well.

We caught THEM in our nets as well. You may not know this, but flying squirrels are incredibly evil and they bite a million times harder than bats do.

The difference between gliding and flight is, very simply, that a flying animal is able to generate thrust. This is why gliders generally hold themselves stiff to maximize their surface area- they don’t have the power to generate it. Fliers do via all that flapping.

Ok, so I’m gonna attempt to do a very, very quick breakdown of basic powered flight mechanics and terminology. Bear with me here.

In order to fly, you need to a) get up into the air and b) stay in the air without falling. Gliders, of course, are falling after they get into the air, unless they happen upon a lucky gust of wind. They’re just falling with style.

Birds, bats, and flying insects (and airplanes) employ what is called an airfoil to help them generate lift- i.e., upward motion. An airfoil is a wing shape that is more sharply curved on the top than the bottom. It looks something like this.

1022px-Wing_profile_nomenclature.svgWhen an airfoil is put with its thicker surface into the wind and angled upwards, something peculiar happens. Due to the sharp curve of the top surface compared to the bottom surface, the air moves faster over the airfoil than under it. This creates less pressure over the top of the wing than underneath it- in other words, it subverts gravity!

That’s how airfoils generate lift. But then why all the flapping? Well, in order for an airfoil to work, you’ve got to have air constantly flowing over the thicker surface. This is called thrust and flapping is what moves that air. Airplanes, of course, achieve thrust with their engines, which is why they don’t have to flap their wings.

There are two main wing motions in animal flight: upstroke and downstroke. The downstroke is what generates thrust by forcefully pushing the airfoil surface through the air. The animal maximizes the surface area of the wing pushing down against the air in this motion. Pushing the wings closer together underneath the body also creates more air pressure that provides additional lift. The upstroke is used to maneuver the wing back into position for the next downstroke, and animals usually minimize the surface area of their wing pushing against the air (to reduce their chances of generating backwards thrust!)

Pigeons are shown here generating both thrust and lift to get up into the air. The thicker part of their wing surrounding bone and muscle is what forms the shape of the airfoil. (Photo by Toby Hudson.)

Pigeons are shown here generating both thrust and lift to get up into the air. The thicker part of their wing surrounding bone and muscle is what forms the shape of the airfoil. (Photo by Toby Hudson.)

Birds and bats both use these mechanics to stay in the air. But it’s the different ways that they approach them that makes it so fascinating.

When you look at videos of birds and bats flying, there aren’t many immediately apparent differences between the motions. In fact, for a long time researchers thought that they flew in essentially the same way: using their wings like rotating paddles.

Anybody who’s ever swum the butterfly stroke will be familiar with the motion: more or less throwing your arms forward to drag the water (or air) behind yourself. Take a moment to think about doing that, and then appreciate the sheer force that bird and bat muscles have to be able to generate.

However, while this is more or less how birds fly, it turns out that bats fly with a much more complex range of motions. They’re just a lot harder to see.

Consider the anatomical differences between bat and bird wings. The first is obvious: birds have feathers, while bats’ wings consist largely of skin membranes. The second is also pretty obvious: bird wings consist of elongated arms and a single finger, while bats use three fingers with the membrane stretched between them. Because the end shape of both is kind of similar, it’s easy to miss how large this difference actually is.

Jh1myIIf you look closely at the above gif, you’ll notice that at several points during flight, the bat actually bends its fingers, which dramatically changes the shape of its wings. Birds do not have joints in their feathers, so they cannot do this. The huge amount of flexibility in bat finger joints is even more apparent when you look back at that picture above of a bat caught in a net- where the wings may appear crumpled are actually where the bat bent down its fingers.

Bats can bend their fingers to the point where their entire wings seem to disappear.

Bats can bend their fingers to the point where their entire wings seem to disappear.

Here's a better look at where all those little fingers get tucked away.

Here’s a better look at where all those little fingers get tucked away.

Flexible joints are not all the bat has in its arsenal. Its actual bones are flexible, due to a lack of calcium in its diet. This means that they deform and reform their shape during flight.

Birds minimize air resistance by rotating their primaries during their upstroke, allowing air to slip between the feathers. Bats, with solid membranes, can’t do this- so they have an even finer means of control. There are lines of muscle present within the bat’s wing membrane that can actually change the stiffness and malleability of its skin. You can see them quite clearly under the skin of our entangled bat friend.

This is a big brown bat (Eptisicus fuscus) by the way.

This is a big brown bat (Eptesicus fuscus), by the way.

These muscles allow the bat to make their membranes flexible during their upstroke to decrease resistance, yet stiff during their downstroke in order to provide lift. It also allows them to change the camber (angle) of their wings on a whim!

This slow-mo video really displays just how incredibly flexible bat wings are.

Bat wings are also covered by millions of tiny, hyper-sensitive hairs that allow the bat to sense air currents and adjust accordingly.

So what does all this control do for the bat?

Well, for one thing, it means they’re not limited by symmetry. Bird wings will almost always mirror each other in shape, while bats may form two different wings shapes at the same time, allowing them to perform some crazy aerial acrobatics. Some insect-eating bats will actually grab an insect by wrapping one wing around it midflight (don’t believe me? You can see it in the beginning of this video!) and then get the insect in their mouth all in a split second, while still flying.

Now, in terms of speed, birds can generally outpace bats. But in terms of maneuverability, bats can fly circles around birds.

The fact that bats’ bones, unlike those of birds, aren’t hollow, and that their skin is heavier than feathers might seem like a disadvantage- but it isn’t. Birds have much more mass in the center of their body than they do in their wings; by contrast, bats have more mass distributed through each wing (12-20% per wing). This means that bats can actually push off their own mass do do things like flip, spin, roll, etc. No bird can stop midflight and flip over to land upside-down, but bats can.

Because they have such fine control over their airfoil shape, bats can also generate lift using less energy than birds. Remember when I talked about minimizing surface area during the upstroke and maximizing it during the downstroke? Bats can bend their fingers and ‘crumple’ their wings as they raise them, conserving energy. Think of it like opening and closing an umbrella. While birds can pull their feathers together more tightly, they can’t exactly clench them like fists.

Decreasing energy costs is good in any situation, but particularly for fliers. It takes a lot of energy to fly. In this case, bats can outcompete both birds and insects for energy efficiency- one study found that nectar-feeding bats, though the largest in size, expended the least energy hovering when compared to both moths and hummingbirds.

So: bats can do all these cool things while flying. Is there a downside? Mmm… yeah. Besides sheer speed, birds do have one major ability that bats don’t: they can walk.

Ok, some bats can walk (four species) and some birds can’t (hummingbirds), but for the most part birds are fairly okay at waddling around on the ground. Most bats… not so much.

We can draw parallels between hummingbirds and bats in this respect, as hummingbirds are among the most maneuverable of all bird species. Selection for increased acrobatics in the air seems to come at the cost of land maneuverability. It makes sense.

And unlike birds, most bats can’t take off directly from the ground. It’s that pesky quadrupedal stance they have. Birds, being bipedal, can push off with their hind legs. Bats can’t do this, aside from a few exceptionally powerful species like the vampire bats and the eastern red bat. Generally if they land on the ground they have to climb up to a vantage point, like a tree trunk, before pushing off.

Interestingly, the other vertebrate fliers- pterosaurs- were also quadrupedal, but could push off from the ground. They used their forearms!

Anyhow, despite their land-based limitations, bat flight is simply incredible. I encourage you to go out on a summer night just after sunset and look to the skies. Maybe you’ll get to witness it for yourself!

Read on: I’ve written more on bats- an overview of bat diversity, a post on species called ghost bats, and a species overview of one of the few walking bats, the New Zealand pekapeka! To view a list of all my nonfiction articles, check the Nonfiction page.


Bat vs Bird Flight

Bat Flight Research Program


Hedenström, A., Johansson, L. C., Wolf, M., Von Busse, R., Winter, Y., & Spedding, G. R. (2007). Bat flight generates complex aerodynamic tracks. Science, 316(5826), 894-897.

Hedenström, A., Johansson, L. C., & Spedding, G. R. (2009). Bird or bat: comparing airframe design and flight performance. Bioinspiration & biomimetics, 4(1), 015001.

Riskin, D. K., Bahlman, J. W., Hubel, T. Y., Ratcliffe, J. M., Kunz, T. H., & Swartz, S. M. (2009). Bats go head-under-heels: the biomechanics of landing on a ceiling. Journal of Experimental Biology, 212(7), 945-953.

Riskin, D. K., Bergou, A., Breuer, K. S., & Swartz, S. M. (2012). Upstroke wing flexion and the inertial cost of bat flight. Proceedings of the Royal Society B: Biological Sciences, rspb20120346.

Swartz, S. M., Iriarte-Diaz, J., Riskin, D. K., Song, A., Tian, X., Willis, D. J., & Breuer, K. S. (2007). Wing structure and the aerodynamic basis of flight in bats. AIAA J, 1.

Tian, X., Iriarte-Diaz, J., Middleton, K., Galvao, R., Israeli, E., Roemer, A., … & Breuer, K. (2006). Direct measurements of the kinematics and dynamics of bat flight. Bioinspiration & Biomimetics, 1(4), S10.

Voigt, C. C., & Winter, Y. (1999). Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats. Journal of Comparative Physiology B, 169(1), 38-48.

Eat My Friends, Not Me: Why Animals Don’t Behave For The Greater Good

*Note: I use the word “suicide” a lot in this article, not to refer to the symptom of depression but to certain animal behaviors.

Animals aren’t like humans, because unlike humans, animals aren’t selfish. Animals work together for the good of their species, even to the point of sacrificing their very lives so that others may live. Take the humble lemming, which, as shown in this Disney animal documentary from the 1950s, will literally jump off cliffs to prevent others from suffering from overpopulation.

By the way? All of the above is bullshit. (Some of you were starting to get worried for a moment there, I know!)

Lemmings do not jump off of cliffs to prevent overpopulation. The footage above, as is now widely known, was faked- the lemmings were actually pushed off the cliffs by the filmmakers. Yes, it’s true.

It may seem logical to assume that animals work for the good of the species- after all, isn’t survival of the species what evolution is all about? Wouldn’t it make sense that animals would evolve mechanisms to make sure that their species is as successful as it possibly can be?

In fact, this ties in to a popular evolutionary theory called “group selection” that had traction (off and on) up until the 1980s, and has even had a resurgence recently. According to group selection theory, natural selection does not work with individuals, but rather on groups. That is to say, a gene that causes a disadvantage to an individual may persist in a population because it provides an advantage to the entire group. Hence our suicidal lemmings.

The problem with the theory group selection is that the basis itself is flawed. We know now that evolution works at the genetic level, and is dependent on whether or not individual animals get to pass on their genes. The word “individual” is key here.

To explain using an example: say that there was a gene that caused lemmings to commit suicide when they noticed that population levels were getting too high for the environment to sustain. Seems grim but logical, right? Well, in order for this gene to actually work, there would have to be some members of the population that didn’t have the suicidal allele. Because otherwise, all of the lemmings would jump off cliffs and that’d be it for the species.

Multiple alleles for the same gene, like the one that determines eye color for humans, can coexist in a species just fine, so that’s not a problem. Here’s the problem with this:

lemmings1See those dots? Let’s pretend that the blue dots are animals with a suicidal allele and that the orange dots are the animals in the population without it. I’ve even given the suicidal allele an edge by having it be more common in the population, increasing the odds that it will be passed on.

Ok, let’s wait a few months and check back in on our population.

lemmings2Wait a minute, what happened? Only orange dots are left!

It really doesn’t matter how widespread the suicidal allele was in the population- it was a suicidal allele. When animals kill themselves, they don’t pass on their genes- so no blue dots lived long enough to give their offspring their suicidal tendencies. Even if they had, the orange dots will always have an infinite advantage over the blue: they have a much better chance of living longer and passing on their genes. A trait which reduces an individual’s chance of successfully rearing offspring would never evolve- because that’s the exact opposite of how evolution works.

Everything is orange.

Everything is orange.

This is where the phrase “selfish gene” comes from. It’s not as though genes are actually capable of being selfish- it’s just that the ones that exist are the ones that were the most successful at propagating themselves in the past. The ones that weren’t successful- even if they were super nice, friendly genes- no longer exist.

Longtime readers of this blog might be quick to point out that I’ve discussed how other supposedly nonreproductive behavioral strategies can be maintained in a population, such as asexual and homosexual behavior. The key difference between these and our theoretical “suicidal” behavior is that asexual and homosexual individuals can still gain indirect fitness benefits by helping their relatives. Committing suicide in order to reduce the population to an environment’s carrying capacity may indeed benefit an entire species, but how is the now-dead animal sure that his sacrifice is benefiting his relatives in particular? A lot of individuals have to die all at once for this strategy to work.

The idea that evolution benefits individual genomes, not entire species, is evident when you study species that have, as I like to call it, evolved themselves into a corner. These are usually hyperspecialized species that have adapted to a single, very unusual habitat or have a very tight symbiosis with another organism. The popular giant panda, for example, is in trouble because its very specific mountain bamboo habitat is disappearing. Likewise, if the special fungi that leafcutter ants farm were to go extinct, so would they (and vice versa) because each provide food for the other.

Which would be a shame, because throwing leaves down on leafcutter ant trails is one of life's great pleasures. (Photo by me.)

Which would be a shame, because throwing leaves down on leafcutter ant trails is one of life’s great pleasures.       (Photo by me.)

Compare the delicate nature of these species with the adaptability and damn-near-impossible-to-eliminate-ablity of a species like, say, a brown rat or cockroach. In terms of success and numbers, those species are certainly winning over the likes of the giant panda, and will still be winning whether or not we turn the coveted bamboo forests of China into parking lots.

If group selection were a viable theory, one might assume that it would guard species against overspecialization. But species overspecialize because evolution doesn’t look ahead: in the short term, specializing can make a species wildly successful. It’s just not a good strategy for the long haul.

I’ll bet that many of us don’t even realize how many of our assumptions about animals end up sounding a lot like group selection. For example: when a prairie dog squeaks at a hawk, it’s to signal the others to run. When birds of a feather flock together, it’s because they have more eyes and ears to watch out for predators for each other. Heck, when any prey species does anything to signal that a predator is near, it’s to signal all its friends and save their lives, right?


I’m sorry to have to say this, but by human standards, many animals are just terrible people.

I’m not saying animals can’t behave altruistically- i.e., for the sake of others to the detriment of themselves- they do, all the time. However, animals generally behave altruistically because, in the end, there is something in it for them. Or at least their genetic material.

Take those famous prairie dogs. Much has been made of their complex predator alarm system- different calls for different types of predators, and even the distance, looks, and behavior of said predators. Upon hearing these hyper-specific calls, the other prairie dogs in the colony know which escape strategy to use.

Super cool, right? And given that the prairie dogs who first give the alarm are likely putting themselves at risk by making themselves more noticeable by predators, it’s a pretty selfless act. With one major caveat. Those selfless rodents are far less likely to call out if none of their close relatives are in danger.

It comes down to protecting your own genetic material once again, whether or not it’s housed in your own body. And this is true of practically all species that use alarm calls- and more often than not, these alarm calls can be used for even more selfish reasons. Great tits and other birds will frequently give alarm calls not but because a predator is coming- but because they want to scare their larger companions away from the food. Some species of antelope even fake alarm calls to keep females nearby. If a female starts losing interest in a male topi’s advances, he snorts as though a lion is nearby to scare her into moving close to him again.


Some animal signals that we’re used to thinking of as alarm calls or warnings for others in the group are actually nothing of the sort. Those of us in the eastern U.S. are acutely familiar with the white-tailed deer, and of the bright white tail that gives them their name. Well, the tail raising behavior is not, as is commonly assumed, a means of warning others in the herd. It is instead a communication to the predator– a way of saying “I see you, so pick on the guy without his tail up.” The fact that other deer may run at the sight of this is a side effect. The signal’s not meant for them.

There's only one wolf this signal's aimed at, if you know what I'm saying. (Photo source.)

There’s only one cougar this signal’s aimed at, if you know what I’m saying. (Photo source.)

A more dramatic version of this is found in gazelles, who perform a behavior known as stotting (or pronking, or pronging). A stot is a vertical leap, which the deer perform when they spot a predator. Stotting actually can slow down gazelles when they’re fleeing, since it’s literally just leaping straight up, but that’s kind of the point: not only are the gazelles showing the predators that they’ve seen them, but they’re proving that they’re fit enough to risk idiotic vertical leaps while they’re running away.

And I do mean idiotic.

Why are we so sure that stotting is a signal meant for the predator and not the other gazelles? Well, for one thing, gazelles stot more when they see coursing predators- your wild dogs and your cheetahs- than they do when they see ambush predators- your lions and your leopards. It makes sense, because in a flat out chase, a signal of how much endurance you have might get the predator to go after a weaker-looking guy. But in an ambush, you’d better dispense with the hopping and get the hell out of the strike zone. Companions be damned.

And as a matter of fact, whether or not an animal stots is a pretty good predictor of whether or not it’s going to survive an encounter with a predator. If you’re too tired to stot, you are pretty much doomed. So you can actually think of it as a kind of favor to the predator, when it comes right down to it. It shows them which individuals they’re going to have a shot at catching, and which they aren’t.

If we’re going to be honest with ourselves, most prey animals would very much prefer that one of their friends gets eaten than the predator go hungry anyway. Because a hungry predator will attack again- while a well-fed predator grants them a reprieve.

So, let’s come back to a fundamental principle here: why do so many prey animals like to live together in large groups? Most ungulates, for sure, but also flocks of birds, schools of fish, swarms of midges… you get the idea.

To understand why this happens, first you have to understand the very real risks this generates for the animals in question. Ever tried to spot a lone sardine in the open ocean? Well, how about a school of thousands? One is a lot easier to find than the other. And predators find them more easily too- so if grouping up is an anti-predator defense, there has to be a damn good reason for it.

The “many eyes” theory is a popular one: it suggests that animals in large groups can trade off the job of looking for predators with others as the day goes on, so that at some point everybody has a chance to relax and feed. The problem with this theory is that a lot of animals are jerks and don’t pull their weight when they don’t have to. In bighorn sheep, ewes with calves spend a lot more time looking for danger than ewes without calves do. In fact, if there are a lot of lambs in a group, the lamb-less ewes spend even less time looking out for predators, because the predators are more likely to go after the lambs than them. Isn’t that sweet.

In general, the rule seems not to be so much “more individuals, more vigilance,” but rather “at-risk individuals spend a lot of time looking for predators and the others mooch off of their efforts.” So while big males and females without young benefit from having more eyes in a herd, in the end, mothers and calves might not.

Let’s look at a couple facts. As predator risk increases, herd size tends to grow larger, and the space between individuals gets smaller- and interestingly enough, individuals that look like each other tend to segregate from those that look different. There’s a moral lesson in that somewhere, but we ain’t about morality here on Koryos Writes.

The most crucial fact of this is the spacing between individuals. If you’ve never seen oceanic predators all teaming up on a “bait ball” of small fish, it’s pretty amazing.

By watching this video, you might feel that something’s off about the way those herring are moving. Namely, why do they all stay in one place, so close together, so that at the end a whale pops up and managed to scoop a huge proportion of them into its gullet? It doesn’t seem like the, er, smartest strategy.

Guess what: it’s not. Not for the group, anyway. These animals probably would be better off, on the whole, if they moved the heck away from each other and all swam in different direction. So why don’t they?

The answer, as you may suspect, is that while this behavior is bad for the whole group, it can have extremely positive effects for a number of lucky individuals. That is why the reigning theory behind this behavior is called selfish herd theory.

Selfish herd theory states this: that when a hungry predator sees one prey animal, that’s the one he’s going to attack. 100%. But when a predator sees two animals side by side, each animal’s chance of being attacked decreases (in a perfect world) to 50%. Three animals side by side? Hoo boy, the risk goes down to 33% each. I like those odds a lot better.

Of course, not all spots in a herd are created equal. The very safest places in a herd are right in the center, surrounded by other delicious-looking targets on the outside. This is why the center of a herd is quite a coveted spot to be, and why you will actually often find the most socially dominant members of a prey group not out in the lead, but in the center.

In the video below, you’ll see the results of a study where researchers attached GPS trackers to sheep (red) and a herding dog (blue). Observe the way the sheep immediately bunch up when the dog gets close.

Those on the outside of the herdrun far more risk of being picked off, and the danger only increases the farther they lag behind their conspecifics. So when somebody spots a predator, they don’t separate- they bunch up, all attempting get to the center. It doesn’t matter how bad this can get for the group as a whole, since the benefits for those lucky few are astronomical. So long as their behavior of sticking to the center means they get more genes out- which it does- they’re going to keep producing babies with a stick-to-the-center mentality. And that’s why they call it a selfish herd.

Now, I left a few things out of this very complex topic: while there are a very significant number of downsides for prey to live in large groups, there are some upsides: less time is devoted to finding food individually (though you’ll then have to compete for it) and it’s a lot easier to find a mate.

Similarly, other theories have decent support as a reason for why animals gang up. The predator confusion hypothesis suggests that predators get more confused as the number of targets they have to look at increases (at least in small-brained predators like sticklebacks). Also, some herds do use their numbers as a means to gang up on predators- cape buffalo are one famous example. However, this depends on how big you are compared to your predator.

The point is that selfish herd theory doesn’t explain EVERYTHING about why prey animals group together. But it’s a pretty big factor.

A factor called “please eat my friends instead of me.”

Read on: To become even more disillusioned about the purity of nature, try my article about animal masturbation. To learn more about animals that evolve in really stupid ways, try chase-away sexual selection or brood parasitism. And here’s where I talk a bit about how traits like homosexual and asexual behavior can be passed on genetically.

References and Further Reading

Beauchamp, G. (2007). Vigilance in a selfish herd. Animal behaviour, 73(3), 445-451.

Bro‐Jørgensen, J., & Pangle, W. M. (2010). Male topi antelopes alarm snort deceptively to retain females for mating. The American Naturalist, 176(1), E33-E39.

Burger, J., Safina, C., & Gochfeld, M. (2000). Factors affecting vigilance in springbok: importance of vegetative cover, location in herd, and herd size. Acta ethologica, 2(2), 97-104.

Caro, T. M., Lombardo, L., Goldizen, A. W., & Kelly, M. (1995). Tail-flagging and other antipredator signals in white-tailed deer: new data and synthesis. Behavioral Ecology, 6(4), 442-450.<

Childress, M. J., & Lung, M. A. (2003). Predation risk, gender and the group size effect: does elk vigilance depend upon the behaviour of conspecifics?. Animal behaviour, 66(2), 389-398.

FitzGibbon, C. D., & Fanshawe, J. H. (1988). Stotting in Thomson’s gazelles: an honest signal of condition. Behavioral Ecology and Sociobiology, 23(2), 69-74.

Hoogland, J. L. (1995). The black-tailed prairie dog: social life of a burrowing mammal. University of Chicago Press.

Hoogland, J. L. (1996). Why do Gunnison’s prairie dogs give anti-predator calls?. Animal Behaviour, 51(4), 871-880.

King, A. J., Wilson, A. M., Wilshin, S. D., Lowe, J., Haddadi, H., Hailes, S., & Morton, A. J. (2012). Selfish-herd behaviour of sheep under threat. Current Biology, 22(14), R561-R562.

Møller, A. P. (1988). False alarm calls as a means of resource usurpation in the great tit Parus major. Ethology, 79(1), 25-30.

Morrell, L. J., Ruxton, G. D., & James, R. (2011). Spatial positioning in the selfish herd. Behavioral Ecology, 22(1), 16-22.

Quinn, J. L., & Cresswell, W. (2006). Testing domains of danger in the selfish herd: sparrowhawks target widely spaced redshanks in flocks. Proceedings of the Royal Society B: Biological Sciences, 273(1600), 2521-2526.

Reluga, T. C., & Viscido, S. (2005). Simulated evolution of selfish herd behavior. Journal of theoretical biology, 234(2), 213-225.

Rieucau, G., & Martin, J. G. (2008). Many eyes or many ewes: vigilance tactics in female bighorn sheep Ovis canadensis vary according to reproductive status. Oikos, 117(4), 501-506.

Taylor, R. J., Balph, D. F., & Balph, M. H. (1990). The evolution of alarm calling: a cost-benefit analysis. Animal behaviour, 39(5), 860-868.

Wiley, R. H. (1994). Errors, exaggeration, and deception in animal communication. Behavioral mechanisms in evolutionary ecology, 157-189.

The Marine Reptile Timeline

The new Jurassic World trailer made me want to learn more about marine reptiles, so that’s what this post is all about.

When you hear the phrase “marine reptile,” your first thought is probably something along the lines of a marine iguana, sea snake, saltwater crocodile, or sea turtle. And you wouldn’t be wrong. Those are all reptiles that spend a good amount of time in the water.

A marine iguana doing as marine iguanas do. By Peter Wilton (Marine iguana  Uploaded by Magnus Manske) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

A marine iguana doing as marine iguanas do. (Photo by Peter Wilton.)

Those of you with a dab more prehistoric knowledge will also probably think of some extinct marine reptiles- your plesiosaurs, ichthyosaurs, mosasaurs, et cetera. Those of us who grew up with any knowledge of early 2000s viral videos will probably think of Liopleurodon thanks to Charlie the Unicorn.

But wait, some of you will now be saying, aren’t the liopleurodons and their long-necked brethren just, like, water dinosaurs?

This is a common misconception. There were no aquatic non-avian dinosaurs that we know of  (though the reconstructed Spinosaurus might be a contender). Liopleurodon was much more closely related to modern lizards than to any dinosaur. However, not all marine reptiles are lizards, obviously- they are not a monophyletic group (meaning, they are not all on the same branch of the family tree). The moniker ‘marine reptile’ is kind of misleading, as is, actually, the word ‘reptile.’

Let’s quickly look at a vertebrate phylogeny.


The green area highlights branches containing animals commonly known as reptiles. As you can see, it does not perfectly cover any one section of the phylogeny. (Pisces = fish, Synapsida = mostly mammals, Testudina = turtles, Lepidosauria = lizards, snakes, and tuataras, Crocodylia = crocodilians, Aves = birds. Dinosaurs are not shown because this is a living phylogeny, but they would be just under Aves.)

I already mentioned that marine reptiles include sea turtles, crocodiles, and marine iguanas, so that means that marine reptiles actually appear independently in three different branches of this phylogeny. This is similar to how marine mammals like seals and manatees and whales all evolved independently of each other, though turtles and crocodiles are much more distantly related than any pair of mammals.

If we ignore freshwater reptiles and only focus on their seagoing relatives, there are about forty living species of marine reptiles today, and surprisingly, most of them are sea snakes. (Sea snakes are not eels, before anyone asks. Eels are fish, sea snakes are snakes.)

Did you know that most sea snakes give live birth? (Photo by Craig D.)

Did you know that most sea snakes give live birth? (Photo by Craig D.)

However, this is really just the tip of the iceberg. Before marine mammals took over the water- and became some of the largest lifeforms ever to exist- there was a very long history of diverse and impressive marine reptiles.

Quick disclaimer: a lot of the taxonomic relationships of these extinct reptiles are hotly in dispute, and as such, there are many conflicting theories out there about their placement. I did the best I could with the info I found, but please take it all with a grain of salt.

Now, let’s go back to the mammal-free seas!

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White-Tailed Deer Overpopulation in the United States


If you live in the suburbs of the Northeastern US like I do, on any given day you might be able to look out your window and see a herd of deer like the one pictured above. In my neighborhood in particular, I am surprised if a day goes by where I don’t see any.

In 1930 the US white-tailed deer population was down to about 300,000. Today, estimates of how many there are range as high as about 30 million. That’s a 1,000-fold increase in less than 100 years.

What would an ideal number of white-tailed deer be in the US? Scientists estimate the average carrying capacity is about 8 deer per kilometer. The current average? Up to 100 deer per kilometer.

The shift in the white-tailed deer population can be attributed to many factors. In the 1920s the species was actually nearing extinction due to overhunting before government protection programs and national parks sought to save it. You could say that they succeeded. Unfortunately, a number of factors are now leading the deer population to spiral out of control. These include:

  • No predators. Wolves, cougars, and grizzlies, which all once preyed on old, sick, and newborn deer, are now extinct in most states, and much of their former habitat is gone. However, the increase in human population will not stop the deer because…
  • Deforestation actually helps the deer. The white-tailed deer is a species that flourishes in “edge” habitats: that is, habitats along the edges of forests and roadways, as well as newly-planted lawns. This is why they have been so explosively successful in the suburbs. Which also means…
  • Hunting rates are going down. On average, about 6 million deer are killed each year by hunters, though this number is decreasing. By contrast, the deer population will double every other year under ideal conditions; the latest estimate suggests that 12 million fawns were born after the last hunting season. And this number will keep increasing because…
  • Due to the fact that they preferentially graze on disturbed or edge habitats, white-tailed deer populations naturally fluctuate. As such, they have evolved few methods of self-regulation (such as birthing fewer fawns in crowded conditions).

So there are a lot of deer and the population is still growing. The impacts this has are not just the annoying ones that I see every day (deer poop everywhere, deer carcasses all over the roads, destroyed gardens, and the occasional deer attack).

Deer in the US eat 15 million tons of vegetation each year, which costs about $248 million in damage to crops and landscaping in the Northeast alone. About 150 people per year are actually killed due to car collisions with deer. Furthermore, deer carry deer ticks, which can transmit lyme disease to humans.

But the impacts are not limited to us. Native ecosystems are bearing the brunt of the damage. A study on one forest in Pennsylvania found that over half of all plant species diversity had vanished thanks to hungry deer. Other studies suggest that deer prefer eating native to exotic plant species, which facilitates the spread of invasive plants.

This can lead to a cascade of effects on other animal species. Nesting bird populations drop due to the loss of certain tree species (the deer like to eat the new saplings). Insect species, particularly caterpillars, may lose their food sources. Conversely, biting flies and other parasites that prey on deer will increase.

What we should do about the deer overpopulation has been a highly divisive issue in the US; specifically between those who favor lethal vs. nonlethal methods. There is limited success with methods such as fertility control, but these successes are mostly found in closed populations (i.e., fenced in or isolated) and take a long time to take effect.

Lethal methods also have their pros and cons. The possibility of reintroducing wild predators of deer in parts of the US where they are now extinct is often raised and just as often vetoed, given that the bulk of the deer population lies smack dab in the middle of the suburbs.

Similar concerns are raised when people bring up hunting; furthermore, hunters must be advised to take does rather than trophy bucks or they will not significantly affect the population. Studies have shown that controlled hunting programs are effective over small areas, but the effects are mixed over larger ones.

While people argue over what the best way to manage deer is, the population continues to grow and grow, leading to an increase of diseases (such as epizootic hemorrhage disease, which can also spread to livestock) and starvation.

With deer populations going well over carrying capacity in many areas, the risk of population crashes grows. While a crash- which dramatically decreases the number of animals- sounds like it might be a good thing in this case, crashes can be catastrophic. In one famous reindeer crash on St. Matthew island, 95% of individuals died in a single winter.

That, however, is the worst-case scenario, and since few deer populations are so constrained, the more likely one is that deer populations will eventually strike a kind of limbo- not increasing very much but still heavily overpopulated, and constantly on the brink of starvation.

In this case, what is the correct thing to do? The longer we wait, the more damage is done, not just to people, but to the local ecosystem as well. But methods like contraception take several years to really show positive effects, while hunting has to be carefully managed in order to be effective. And this isn’t even bringing in the “moral” aspect of hunting versus nonlethal methods. Yet either way, many, many deer are going to die, and the only way to improve their- and our- quality of life is to dramatically reduce their population.

This isn’t the first time I’ve written about the issues with animal overpopulation- check out my post on rodent plagues. I’ve also written an article about deer with fangs.

To see a list of all animal articles that I’ve written, head to the Nonfiction section of this site.


Alverson, W.S., D.M. Waller, and S.L. Solheim. 1988. Forests too deer: edge effects in northern Wisconsin. Conserv. Biol. 2: 348–458.

Brown, T. L., Decker, D. J., Riley, S. J., Enck, J. W., Lauber, T. B., Curtis, P. D., & Mattfeld, G. F. (2000). The future of hunting as a mechanism to control white-tailed deer populations. Wildlife Society Bulletin, 28(4), 797-807.

Eschtruth, A. K., & Battles, J. J. (2009). Acceleration of exotic plant invasion in a forested ecosystem by a generalist herbivore. Conservation Biology, 23(2), 388-399.

Horsley, S. B., Stout, S. L., & DeCalesta, D. S. (2003). White-tailed deer impact on the vegetation dynamics of a northern hardwood forest. Ecological Applications, 13(1), 98-118.

Insurance Institute for Highway Safety. 2009. Deer-vehicle collisions: no easy solutions but some methods work or show promise. Advisory No. 31.

Iowa State University, 2012. Epizootic hemorrhage disease in deer and cattle.

Kilpatrick, H. J., & Walter, W. D. (1999). A controlled archery deer hunt in a residential community: cost, effectiveness, and deer recovery rates. Wildlife Society Bulletin, 115-123.

Patterson, B. R., & Power, V. A. (2002). Contributions of forage competition, harvest, and climate fluctuation to changes in population growth of northern white-tailed deer. Oecologia, 130(1), 62-71.

Peek, L.J., and J.F. Stahl. 1997. Deer management techniques employed by the Columbus and Franklin County Park District. Ohio. Wildl. Soc. Bull. 25: 440–442.

Piesman, J. (2006). Strategies for reducing the risk of Lyme borreliosis in North America. International Journal of Medical Microbiology, 296, 17-22.

Rooney, T. P., & Waller, D. M. (2003). Direct and indirect effects of white-tailed deer in forest ecosystems. Forest Ecology and Management, 181(1), 165-176.

Rooney, T. P., & Dress, W. J. (1997). Species loss over sixty-six years in the ground-layer vegetation of Heart’s Content, an old-growth forest in Pennsylvania, USA. Natural Areas Journal, 17(4), 297.

Rooney, T. P. (2001). Deer impacts on forest ecosystems: a North American perspective. Forestry, 74(3), 201-208.

Roseberry, J. L., & Woolf, A. (1998). Habitat-population density relationships for white-tailed deer in Illinois. Wildlife Society Bulletin, 252-258.

Rutberg, A. T., & Naugle, R. E. (2008). Population-level effects of immunocontraception in white-tailed deer (Odocoileus virginianus). Wildlife Research, 35(6), 494-501.

Seagle, S. W., & Close, J. D. (1996). Modeling white-tailed deer< i> Odocoileus virginianus population control by contraception. Biological Conservation, 76(1), 87-91.

U.S. Department of the Interior, Fish and Wildlife Service, and U.S. Department of Commerce, U.S. Census Bureau. 2006. National Survey of Fishing, Hunting, and Wildlife-Associated Recreation.

Creepy Creatures #5: PLANTS SCARE ME

We’ve done bats. We’ve done rats. We’ve done creatures of the deep and we’ve done toad maggots that creep. But in all honesty, do you know what scares me more than any of that?


Ok, hear me out. I mean, you probably don’t spend a lot of time thinking about plants, much less being terrified of them. After all, they’re stationary, and they don’t have any mouths or eyes or brains, and any fool with an axe can go chop down a tree.

I mean, it's not like trees can drive.

I mean, it’s not like plants can drive.

But listen… there’s a major difference between plant biology and animal biology. I’m not talking about stamens and pistils and all that, I’m talking more fundamental. See, what with the whole stem cell research debate, most people generally understand that we are born with stem cells that turn into particular types of cells, like liver or bone marrow. But once those stem cells determine what they can be, they don’t ever change back.*

(*There are some exceptions to this. I own axolotls, after all.)

Plants don’t have to follow that rule. When you take a cutting from a branch of one plant and replant it, it can grow root cells from former branch cells. That’d be like cutting off someone’s leg and having a head grow out of it.

This distinction is important, because it means plants and animals play by very different rules. Most animals are screwed if they lose, say, their heart, but plants can survive incredible amounts of damage to all different parts of their bodies. The tradeoff for this is that plants can’t have parts that are too specialized. They can’t really have centralized brains, because then they would have a single vulnerable spot that they wouldn’t survive losing.

Because they can’t specialize too much, it’s hard for plants to develop things like locomotion. But not being able to walk doesn’t mean that plants don’t move. They just do it very… very… slowly.

The difference in plant and animal motion isn’t just in terms of speed. Animals move by lugging their entire bodies from place to place. Plants move by simply… growing. Getting larger. And larger.

“A flower does not think of competing to the flower next to it. It just blooms.” -Sensei Ogui

The above is a quote that I have seen passed around both facebook and tumblr for quite a while. It is a nice sentiment, and it is entirely wrong. The essentials of life for all plants are sunlight, water, and nutrients, and not one is limitless. No, not even sunlight; unless you grow enough to tower over all other plants in the area, you’ll be stuck struggling in the shade.

A lush and beautiful rainforest is also a savage struggle for resources among thousands of plants.

A lush and beautiful rainforest is also a savage battle for resources among thousands of plants.

Like animals, plants have also come up with crafty ways to compete with one another. One way is to simply kill the competition, or prevent it from ever growing. Many plants utilize a tactic called allelopathy, which essentially boils down to “let’s use chemicals to fuck with our neighbors.”

The black walnut tree is rather jealous over its root space, and will secrete a chemical called juglone into the soil. Not all plants are affected- some have evolved defenses- but for the ones that have not, juglone inhibits enzymes that are necessary for respiration. In other words, it stop plants from breathing.

But that isn’t even the most sinister effect allelopathy can bestow. Botanists are beginning to find that the secret to the success of many invasive plants lies in their aggressive allelopathy. Spotted knapweed, a European species that is now invasive to the US, utilizes a chemical called (-)-catechin to interfere with its neighbors. When another plant takes up (-)-catechin through its roots, the chemical causes a signalling cascade that actually turns off a a number of the genes in each cell it contacts. This means that the cell can no longer produce the proteins it needs to survive, and it dies within the hour.

Allelopathy is not always harmful to neighboring plants, however; in some cases, whether through mutually beneficial co-evolution or one plant sneakily taking advantage of another’s defenses, sometimes plants produce chemicals that help others grow. Sometimes a plant will produce a chemical that has a negative effect on one plant species, but a positive effect on another. It’s a tricky balance.

Some plants prefer a more medieval way of one-upping the competition than by using chemicals, however. These would be the climbing vine species, including the strangler figs. I’ll let Sir David describe what those do.

‘Strangler fig’ really is an apt name.

Perhaps plants very slowly fighting with other plants does not seem particularly frightening to you. But plants are not just affected by plant competitors- they are equally harassed and attacked by animal parasites and predators. A sheep or cow is about as vicious as it gets from a plant’s point of view. And, of course, they have means with which to fight back.

The most obvious of these means is poison- plants will produce phytotoxins (literally, plant toxins) that can cause anything from mild stomach upset or itchy skin all the way to asphyxiation or cardiac arrest. While this is good enough for us to leave certain plants alone permanently, there is a downside for the plants. Firstly, these chemicals are often complex and expensive to produce and build up in the cells; and secondly, animals may evolve resistance.

Some plants have come up with a slightly evil compromise.

I spoke before about how it doesn’t bother a plant so much to lose a few branches, roots, or leaves. So a bit of nibbling by a few herbivores will not cause a great deal of harm to a large bush. But when the number of leaves begins to dip dangerously low, this is another matter, and the plant may have ways to detect this and to take action- and more.

One example of this is oak trees. When caterpillars begin to eat oak leaves, the tree responds by ramping up the amounts of tannin and phenol in their tissue, making the stuff harder for caterpillars to ingest. In fact, the reason why herbivores have to eat so much plant matter- seriously, think about the amount of time a cow spends grazing, then sitting down and chewing cud- is because of this type of defense. As soon as the plant detects that it is being eaten, it turns on its less digestible compounds.

This can cause a normally harmless plant to become deadly. There is a famous case that occurred in the 1980s in which roughly 3,000 kudu inexplicably dropped dead in South African game reserves.

Imagine these, but dead. (Photo by)

Imagine these, but dead. (Photo by Paul Schaffner)

No predator attacked these kudu, and none of them looked sick; indeed, they seemed completely healthy. The culprit was, of course, a plant; acacia trees, which kudu can usually eat without repercussion. The problem was that a drought had killed many of the kudu’s other food sources, forcing them to feed almost exclusively from acacia trees. The trees did not like this, and when they started losing too many leaves, they went on the defensive.

Not only did the trees that were being attacked raise their tannin content to deadly levels (preventing the kudu from digesting any of the food that sat uselessly in their stomachs), but they also released an ethylene gas into the air to communicate with other acacias. When the other trees picked up the signal, they too increased their tannin levels, leading to mass murder of the hapless kudu.

In lieu of a nervous system or the ability to communicate with sound or movement, plants regularly speak to other plants- and animals- via chemicals like these. I am sure most of us are familiar with the phenomenon of sealing fruit in a bag to make it ripen faster. This is because fruit releases ethylene gas as it ripens that signals itself and the rest of the fruit on the tree to keep ripening. Apples and bananas are particularly strong ethylene producers, which is why slow ripening fruit like kiwis ripen faster if kept in close proximity to either of those.

Like the acacia, plants also produce ethylene when they are wounded to stimulate the healing process. Other plants in the area may “listen in” and ramp up their chemical defenses in preparation, whether or not they are the same species.

As I said before, plants can also use these chemicals to communicate with animals in rather surprising way. The tobacco hornworm is a familiar garden pest, and a voracious plant-eater. The tobacco plants that this insect preys on do not waste much time trying to poison their predator. Instead, they send out a cry for help via a volatile chemical compound. And who should answer but the lovely braconid wasp?

The wasp leaves the caterpillar with a few special, hungry friends. (Photo by)

The wasp leaves the caterpillar with a few special, hungry friends. (Photo source)

Yes, as a matter of fact, the plant calls the wasp over to kill the caterpillars. And this is not the only time that plants call for backup; it’s been documented many times, generally with insect predators. And the plants know who to call, too, because they can tell who’s eating them. Different types of herbivore saliva actually enact different defenses. This even extends as far as mechanical damage- if you rip a plant’s leaf without putting any of your saliva on it, the plant may not behave as though it’s being attacked. Those defensive compounds are expensive to produce, after all, and the plant doesn’t want to waste time over a freak accident.

The idea of a plant knowing who’s attacking it can seem ridiculous, considering that plants lack a brain or even a simple nervous system. But plants may know a hell of a lot more than we think they do; and it may be because we are too used to looking at things from an animal mindset. So a plant can’t afford to have a centralized organ for thinking, right? That may not mean it can’t think. It looks as though it definitely doesn’t mean that the plant can’t learn.

M. pudica, known as the “sensitive plant,” is one of the few plants that can display animal-like behavior. This plant actually responds to touch by closing its leaves. It does this not with muscles but via a system of pressure sensors that cause the cells in the leaves to lose their turgidity (firmness).

M. pudica responding to touch.

M. pudica responding to touch.

Some rather recent research on this plant came up with stunning results: the plant appeared capable of learning when a touch was not harmful. The scientists achieved this by dropping water on the plant’s leaves in both high and low light environments. In each case the plant seemed to figure out that it wasn’t worth closing its leaves for the water droplets in a matter of seconds; furthermore, it learned better in the high light condition than in the low light condition. In the same way, food-deprived animals will have more difficulty learning than well-fed animals.

M. pudica didn’t just remember about the water for a few seconds, though. Even a month later, it still appeared to remember that water droplet = not harmful. But when given another stimulus that it wasn’t familiar with, such as a vigorous shaking, the plant closed right up.

How does the plant store memory without a nervous system…? We just don’t know. But this is far from the first experiment to suggest that plants are capable of learning and memory. Other experiments have suggested that plants can remember being tilted sideways after spending a few days in a fridge (the plants respond to tilting by growing in the direction that they think is up).

Plants can actually navigate mazes much more efficiently than many animals can; they do this by growing towards a light or nutrient source. Plant roots ignore nutrient-poor soil patches but spend a lot of time feeding and getting hairier in nutrient-rich patches, just like a foraging animal. Plants will also move (grow) to avoid contact with other plants, and may even be able to tell when other plants are related to them. Some trees will pass on more carbon via fungal networks to their seedlings than other plants, and some plants avoid competing for soil nutrients with relatives but battle with strangers.

There is, in fact, a vast and terrifying body of research that suggests that not only may plants have a kind of intelligence, but it is a kind of intelligence that we are just beginning to tap in to. We are too used to associating ‘behavior’ with mechanical movement to really understand what plants are doing. Because they are behaving- slowly, yes, but with no less drive and intention than many animals. What we store in our brains might be spread out throughout the entire body of a plant, but it is still there, and it is capable of learning.

Imagine this: a movie monster that can basically regenerate any part of its body, that can change its chemical composition on a whim to become toxic, that can call in an army of wasps, for god’s sake. We live with these monsters. They are plants.

Previous creepy creatureFirst creepy creature!

To view a list of all my animal articles, head to the Nonfiction section.

Resources to Learn More


What Plants Talk About

In the Mind of Plants

Plants Behaving Badly (Parts One and Two)


Aspects of Plant Intelligence” by A. Trewavas (warning: it is very, very dense)


Allmann, S., & Baldwin, I. T. (2010). Insects betray themselves in nature to predators by rapid isomerization of green leaf volatiles. Science, 329(5995), 1075-1078.

Bais, H. P., Vepachedu, R., Gilroy, S., Callaway, R. M., & Vivanco, J. M. (2003). Allelopathy and exotic plant invasion: from molecules and genes to species interactions. Science, 301(5638), 1377-1380.

Cooper, S. M., & Owen-Smith, N. (1985). Condensed tannins deter feeding by browsing ruminants in a South African savanna. Oecologia, 67(1), 142-146.

Dudley, S. A., & File, A. L. (2007). Kin recognition in an annual plant. Biology Letters, 3(4), 435-438.

Gagliano, M., Renton, M., Depczynski, M., & Mancuso, S. (2014). Experience teaches plants to learn faster and forget slower in environments where it matters. Oecologia, 175(1), 63-72.

HOVEN, W. V. (1984). Tannins and digestibility in greater kudu. Canadian Journal of Animal Science, 64(5), 177-178.

Ishikawa, H., Hasenstein, K. H., & Evans, M. L. (1991). Computer-based video digitizer analysis of surface extension in maize roots. Planta, 183(3), 381-390.

Jose, S., & Gillespie, A. R. (1998). Allelopathy in black walnut (Juglans nigraL.) alley cropping. II. Effects of juglone on hydroponically grown corn (Zea maysL.) and soybean (Glycine maxL. Merr.) growth and physiology. Plant and soil, 203(2), 199-206.

Kessler, A., & Baldwin, I. T. (2001). Defensive function of herbivore-induced plant volatile emissions in nature. Science, 291(5511), 2141-2144.

Thellier, M., & Lüttge, U. (2013). Plant memory: a tentative model. Plant Biology, 15(1), 1-12.

Trewavas, A. (2003). Aspects of plant intelligence. Annals of Botany, 92(1), 1-20.

Creepy Creatures #4: The Real Ghost Shark

Yes, I already did one “ghost animal” this month, but since SyFy did a movie titled Ghost Shark, I couldn’t pass this up. Because there really is such a thing as a ghost shark.


I haven’t seen Ghost Shark myself, but I’ve been made to understand that it is a modern masterpiece.

I’m not talking about the kind of ectoplasmic sharks that materialize out of slip’n’slides to eat small boys, though. The real ghost sharks are actually not sharks at all, but a group of creatures called a chimaeras.

When I say ‘chimaera’ I am not referring to the creature in Greek mythology, but rather a living group of fish related to sharks. These fellows represent some of the earliest body forms that jawed fishes ever took, right down to the large, placoid scales on the face. Most species also live in the deep ocean, which means that they get that extra dose of horror to their looks.


Chimaera sp.

This is a 420 million year or more order of fish; far older than sharks, which they diverged from 400 million years ago. They were the earliest members of the class Chondrichthyes, the cartilaginous fishes.


The living members of Chondrichthyes are the chimaeras (Holocephali), the sharks (Galeomorphi and Squaliformes), and the rays (Batoidea).

Chimaeras are divided up into three families, the plough-nosed chimaeras (Callorhinchidae), the shortnose chimaeras (Chimaeridae), and the long-nosed chimaeras. (Rhinochimaeridae). That’s a lot of focus on the nose, and with good reason. Chimaeras can have some weird snouts, which makes the members of these three families instantly identifiable.

(Source: Fir0002/Flagstaffotos)

Callorhinchus milii, a plough-nosed chimaera.  (Source: Fir0002/Flagstaffotos)

Close up of Hydrolagus melanophasma, a shortnose chimaera, from Bustamante et al., 2012.


Rhinochimaera pacifica, a long-nosed chimaera.

Here’s a rundown of bizarre physical features that chimaeras have.

Those noses are all covered in specialized sensory organs called electroreceptors that look like small pits. These are most obvious in the shortnose chimaeras, which are sometimes called rabbit or rat fish due to the rodentlike “spotted” appearance of their faces.

The smalleyed rabbitfish, Hydrolagus affinis, makes me uncomfortable.

The smalleyed rabbitfish, Hydrolagus affinis, makes me uncomfortable.

Like sharks, male chimaeras have claspers located on either side of their genital opening. However, they have a third, retractible clasper- on their head. This clasper doesn’t deposit sperm, but does help the male to hold the female’s pectoral fin during copulation.


Head and pelvic claspers of Callorhinchus milii. Those spikes are denticles, i.e., skin teeth. (Photo by Doug Perinne.)

Most chimaeras also have a venomous spine on their pectoral fin that is used in defense. I couldn’t find much about the potency of the venom, but some reports indicate that it creates painful wounds accompanied by swelling in humans.

Rhinochimaera africana is a good-looking dude.

Rhinochimaera africana has a prominent spine and wiggles that big nose around on the ocean floor to detect prey.

Adult chimaeras do not have teeth. The young ones do, but these fall out and are replaced by three pairs of large dental plates in adulthood. They use these to grind up hard-shelled crabs and mussels that they pull up from under the sand.

Dental plates of the spotted ratfish.

Beaklike dental plates in the skull of Hydrolagus colliei. (Source.)

These plates also give them lovely smiles.


Callorhinchus milii again.

Their egg cases are weird-looking. I dunno what else to say about them.



And finally- and perhaps most intriguingly- chimaera skeletons contain traces of a third pair of limbs. Because of their placement in the fishes, this suggests that some of the earliest vertebrates may have had three pairs of limbs and later lost one. Neat!


Chimaera: not super creepy, but definitely weird.

Previous creepy creatureNext creepy creature

To view a list of all my animal articles, head to the Nonfiction section.


Ghost shark (Chimaera monstrosa)

Creatures of the Deep: Chimaera

Black Ghost Ratfish

Long-nosed Chimaera


Bustamante, C., Flores, H., Concha-Pérez, Y., Vargas-Caro, C., Lamilla, J., & Bennett, M. (2012). Primer registro de Hydrolagus melanophasma James, Ebert, Long & Didier, 2009 (Chondrichthyes, Chimaeriformes, Holocephali) en el Océano Pacífico suroriental. Latin american journal of aquatic research40(1), 236-242.

Dean, B. (1906). Chimaeroid fishes and their development (No. 32). Carnegie Institution of Washington.

Didier, D. A., Kemper, J. M., & Ebert, D. A. (2012). Phylogeny, biology, and classification of extant holocephalans. Biology of sharks and their relatives, 2nd edn. CRC Press, New York, 97-124.

Lund, R., & Grogan, E. D. (1997). Relationships of the Chimaeriformes and the basal radiation of the Chondrichthyes. Reviews in Fish Biology and Fisheries,7(1), 65-123.

Patterson, C. (1965). The phylogeny of the chimaeroids. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 101-219.

Previous Creepy Creature article: Blow Your Nose, Toad