23.4a – The New World Monkeys

Out with the old, in with the new. (Common squirrel monkey photo by Geoff Gallice)

A whole new world! A dazzling place you’ve never been! Or so goes the song, but if you’ve ever been to the Americas, North or South, you actually have been there.

Here at last we come to the sorts of animals we imagine when we think of primates — the monkeys. And let me tell you, there are a lot of different monkeys out there. Most of the warm places in the world are crammed full of them. But one type of monkey is not quite like another. Scientists who work on these sorts of things have divided monkeys into two major groups — the old world monkeys, those that evolved in Africa and Asia; and the new world monkeys, those that evolved in central and South America.

The two groups split apart about 40 million years ago, but the curious thing is how that came to happen. After all, 40 million years ago there was no known connection between South America and Africa or Asia. We know that monkeys originally developed in the old world, so how did they come to be in the new?

The obvious thought is that they crossed the land bridge that once existed between Russia and Alaska, the same way humans eventually did, but we don’t think that’s what happened. There is absolutely zero fossil evidence to suggest that monkeys ever moved through North America or Siberia. And besides, North and South America were not yet connected, and wouldn’t be for tens of millions of years, so if monkeys had come through North America they would have been forced to stay there for a long time. As far as we know, that’s not what happened.

But there’s another way they could have made the journey. We have no way to know for certain, but the idea is that those ancient monkey pioneers that made the trip to South America to become a new type of monkey actually came from Africa, and crossed the Atlantic Ocean.

Now the Atlantic Ocean is very big, so I understand if you’re skeptical. It’s not as though the monkeys of 40 million years ago could build boats. But remember that South America and Africa are moving apart from one another, which means that the Atlantic was quite a bit smaller back then. It was still, however, a very formidable stretch of ocean, on the order of a thousand miles wide, if not wider.

The current theory goes that there existed at that time a number of islands between Africa and South America, stretching across that growing ocean. This is certainly possible, and the ocean levels of the world were a bit lower back then as well, so there may have been islands. The monkeys may have more or less accidentally crossed them over the course of many thousands of years, populations swept westward on floating debris and material with the currents (which were also different then than they are today).

So it came to be that monkeys, those adaptable, adorable, terrible creatures, set foot on a brave new world and took to the great jungles of South and central America. But what makes a new world monkey special, besides its geographic location?

Is it the fabulous whiskers? (Emperor tamarin photo by Brocken Inaglory)

New world monkeys are typically a little smaller than their old world counterparts, but the nose is where it’s at. Just as we split wet-nosed primates apart form dry-nosed primates, monkeys too are divided by what’s around their nostrils. New world monkeys have flatter, more narrow noses than the old world variety, and their nostrils face to the side instead of down or straight ahead. The new world monkeys also have prehensile, grasping tails, while the old world monkeys are stuck with tails that can’t grasp a thing. To balance this out, most new world monkeys do not have opposable thumbs, either, while the old world monkeys — and by common evolutionary ancestry, us — all have that useful trait.

There are five families in the new world monkey group, and we will examine each of them in their turn. Among them we will find monkeys that swing, monkeys that howl, and the smallest monkey in the world. The new world monkeys are unconscionably addicted to trees, and they show it in some of their names. We’ll have squirrel monkeys, owl monkeys, spider monkeys, and more. But enough with the introduction. It’s time to monkey around.

22.2a – The Anteater

A nose for nummies. (Giant anteater photo by Malene Thyssen)

The South American grasslands. Night. Vast wild fields roll away in every direction, scattered with countless tall termite mounds, their walls so thickly-built and cemented together that one might almost mistake them for rocks. And shambling out of the darkness across the fields — a strange and shaggy creature that seems almost to have no head, only a neck that gets longer and narrower until it reaches a blunt point. A giant anteater.

The animal walks on its knuckles, but when it stops before the nearest termite mound it unfurls massive, powerful claws like those of a fearsome predator. And it is a fearsome predator, in its way. With great gouges in the hard walls, the giant anteater rips chunks from the earth and exposes the many tunnels of the busy insects. Protected by its shaggy hair from any bite or sting an insect might offer, the creature reveals that what seemed to be its too-long neck is actually simply its head — a head that is narrower than the neck it sits on. With such a long and narrow snout it can shove its mouth directly into the termite tunnels.

Its tongue, longer than its head and attached to its sternum deep in its chest, flickers in and out almost faster than the eye can see, up to two-and-a-half times per second, shooting down into the termites’ home and through its many tunnels. The tongue is a marvel, not only fabulously long but covered in thousands of tiny hooks and coated with a sticky saliva, which combine to snatch up any termites it encounters. The insects it swallows are pulled alive into the anteater’s stomach where hard plates and any dirt or sand accidentally swallowed help to crush and grind the insects into a digestible and nutritious paste.

The termites are no fools, and within a minute they have begun to organize themselves to attack the giant invader, but the anteater is careful. By the time that minute has passed it has gobbled up as many termites as it can and then stops. There are many termites left, but this particular mound is now potentially dangerous. But there are always more mounds, and the creature will visit as many as 200 different termite nests this night before it has eaten enough to see it through the day, which it will spend sleeping in the shade and lowering its body temperature to require less energy.

The giant anteater is the most recognizable of the anteaters, which are closely related to sloths even though they look almost completely different. There were once many different types of anteaters, but competition from species migrating south from North America in the past three million years has reduced the anteater to a mere four species found in central and South America. The giant anteater is the largest, but is also the only one that lives its entire life on the ground.

Consider the silky anteater. The most distant cousin in the anteater family, it is the size of a mere house cat, if not smaller, and can be found in dense jungles instead of grasslands. The silky anteater lives its entire life in the trees, just like a sloth, and it has a prehensile tail to help it climb around in search of insects. But despite its much different appearance and lifestyle, it still employs the same feeding strategy, using a long tongue to lap up insects for nutrition. It sleeps by rolling itself into a ball in a tree, often in such a way that it looks like a seed pod and will thus be left alone.

The littlest anteater, here refusing to show off its powers of camouflage. (Silky anteater photo by Eveha)

Between these two extremes are the tamanduas, the northern tamandua and the southern tamandua to be precise. They are medium-sized anteaters that also have prehensile tails, but they split their time between the ground and the trees. They eat ants and termites with the best of them, but aren’t picky about where to find them.

Fact: ants taste better when eaten upside-down. (Northern Tamandua photo by Dirk van der Made)

Anteaters are not gentle creatures. They aren’t going to storm your home and break down your walls in search of insects, but if you threaten an anteater it will rear up on its hind legs like a bear and will show you exactly how powerful its enormous claws are. Jaguars and large eagles are typically the only animals tough enough to tackle anteaters. They aren’t very nice with one another either. Anteaters are all solitary creatures, and will fight one another if there is a question of territorial rights. When in a scrum, one anteater might even try to climb on top of the other’s back to get an advantage with those claws. Anteaters mean business.

Bonus fact — anteaters are also known as ant bears, though they aren’t related to bears at all, and the scientific name for the anteater group, Vermilingua, means “worm tongue”.

22.1a – The Sloth

Getting the hang of it. (Photo by Masteraah)

Ah, the sloth. Has any animal’s name ever been so efficiently descriptive, so elegantly appropriate? It’s all right there, one word, five letters — sloth.

Sloths are curious creatures found in the jungles of central and South America. The word “sloth” existed before the scientific community knew about them, a word that meant slow, lazy, lagabout, mud-for-bones, or any number of terms both real and perhaps imagined by the author that come round to the same concept — just plain doesn’t do much. Like a teenager on summer vacation, the sloth fits this term perfectly, so perfectly that we slapped the word right on it as a name.

These creatures are highly distinctive. They are shaped somewhat like large monkeys with their long arms and flat faces, but they are not in any measurable way related to primates. As you know, they are most closely related to anteaters. It’s only that long arms and a generally monkey-like body shape are best suited for climbing in trees, and that’s what sloths do, so this is what they evolved to look like.

Sloths in fact spend almost their entire lives in trees, because that’s where they are safest from predators. But there are many predators in South America that can also climb trees, from the jaguar to large snakes, so what’s this all about?

The key to life as a sloth is in the name. Sloths are known for moving very, very, extremely, quite rather incredibly very slowly. But it’s not laziness. The slowness of a sloth is in fact its greatest defense against predators.

“Don’t mess with me. I’m warning you, if you do, I will sit here. I will sit here so hard, you won’t even know what didn’t hit you.” (Photo by Stefan Laube)

If that makes no sense to you, you’re just not thinking like a sloth. When you don’t move, you don’t attract attention, and when you don’t attract attention, predators don’t try to eat you.

With this in mind, sloths have taken the fine art of not moving to new levels. They spend about ten hours a day sleeping, and the rest is spent hanging upside-down from branches and either not moving or very, very slowly reaching out for leaves to eat. A sloth will only carefully move around in a tree to find new food, or for a bathroom break. When a sloth needs to do its business, it doesn’t simply squat and let it go off the side of a branch. No, the sloth is a more refined creature. About once a week a sloth will very slowly climb down to the ground and relieve itself, then very slowly climb back up.

In fact, scientists have wondered why they do this, because it’s easier to just go from the tree and let it drop, not to mention safer. We don’t really know for certain. Some think it is how sloths find each other for breeding purposes; others think the sloth is worried that going from the tree will make too much noise and attract a predator; still others think the sloth is trying to nourish the tree by burying its excrement near the trunk, thereby helping its own food supply. Or maybe they’re just really fussy. Who knows?

The best part of all this is that it means not only that the sloth digests its food very slowly, but that it stores its excrement inside its own body until it’s ready to do its business. If you kill a sloth close to its bathroom day, there’s a good chance that up to one-third of its body weight will be feces and urine that it was waiting to get rid of. So have fun with that.

This lifestyle serves the sloth very well. For one thing, when you don’t move much you don’t use energy, which means you need to eat less, which means you need to move less. It’s a very happy cycle. For another, the sloth is perfectly adapted for hanging upside down in trees. It is the only mammal with hair that grows toward the body instead of away from it. Look at your arm — the hairs all grow out toward the hand. Look at a dog’s leg — the hairs grow down toward the feet. Not so for the sloth. Its hairs grow the opposite direction, back toward the body’s core, because that way it will still protect against rain when the sloth is hanging upside-down, which it nearly always is.

In addition, sloths have long, curved claws that are not for digging or fighting — though they will take a swipe at you if you threaten it — but for hanging. The claws allow the sloth to hang without any effort, no use of muscle at all. They just dig the claws in, let themselves relax, and hang. This is so effective that even human poachers don’t bother sloths as much as they otherwise might. If you shoot a sloth while it’s hanging, it will simply keep hanging even when it’s dead, held up by its claws, and the poacher would have to climb up and get it. It’s the ultimate post-death screw-you.

Even a sloth that dies a natural death, say from old age, can sometimes remain hanging. They give birth while hanging upside-down, they eat upside-down, they sleep upside-down. To a sloth, the world looks crazy and backward when they stand up straight.

You might not expect it, but sloths can swim. However with all this talk of how slow they are, you might be wondering, really, how slow are they? A sloth in extreme danger of its life will turn up the volume and dash about at an incredible 13 feet per minute. Yes, per minute. Try moving that slowly across your living room without going insane. But remember, that’s only the speed of a really terrified sloth. Normally they only move half that fast at best, and usually even slower.

Two hours later, it finished this bite. (Photo by Fruitwerks)

There’s even a bit more to a sloth’s defense system than sheer slowness, though. They also have camouflage, and it’s about the grossest camouflage you can think of.

Each sloth is essentially its own slow-moving ecosystem. Their hair is host to a number of bacterial colonies that just love sloths, love them so much that a sloth is the only place they will grow, and each baby sloth gets its own bacterial colony from its mother. The bacteria go nuts and cover the sloth’s hair and skin with patches of colour that help the animal blend in with the branches. In exchange for making it harder to see, the sloth lets the bacteria live on its body forever. The bacteria also tends to attract insects, and so you might also find plenty of happy bugs snuggled up with the sloth. They all get along famously, but for the love of God don’t try to pet one.

There are two basic types of sloths alive today, the two-toed sloths and the three-toed sloths. Despite their similar appearance in all things not toe-related, these two types are not very closely related at all.

All sloths have three toes on the back feet, but the two-toed sloths have only two toes on the front feet. These two types of sloths have been evolutionarily separate for more than 35 million years, which is a very long time for two things to be apart and yet still look so similar. The two-toed sloths are much more closely related to the extinct giant ground sloths than to their three-toed distant cousins.

We don’t even actually know what three-toed sloths are related to, or how they came to be. Their line on the tree of evolution is drawn in the shape of a question mark. But it is believed that the two types of sloth evolved independently from ground-dwelling sloths, and that it is sheer coincidence and convergent evolution that they look and behave so much alike. They even both do the inexplicable bathroom thing.

There is, however, one other major difference between the two types of sloth, and it’s a difference that sets each of them apart from all the other mammals as well. For whatever reason, almost every single mammal has seven neck bones, known as cervical vertebrae. You have seven, I have seven, your cat has seven, your hamster has seven, the elephant that hopefully didn’t just step on your hamster has seven, even the long-necked giraffes and the no-neck whales have seven.

But sloths? Sloths said no, no way, that won’t do, and they said it in opposite directions. The two-toed sloths have six neck bones; the three-toed sloths have nine. Why? No one knows. It’s preposterous and mysterious. They don’t need more or fewer neck bones. They’re both practically the same animal, why did they go different directions in terms of more or fewer? What purpose does it serve? Are they just trolling scientists?

We do actually have some idea how this happened, even if the result serves very little purpose. With nine neck bones the three-toed sloth has a more flexible neck than other creatures, but it doesn’t need it; nor does the two-toed sloth needs its more rigid neck. But it comes down to genes.

It turns out that the reason every other type of mammal has seven neck bones, no matter how big or small its neck gets, is that the gene that controls how many neck bones we have is the same gene that helps determine how our nervous systems and our cells grow. If that gene were to change our number of neck bones, there’s a good chance that it would also give us brain problems and cancer, which would keep us (or any other mammal) from passing its different-number-of-neck-bones gene along to any offspring.

So how did the sloth get away with it? It is useful to consider that one other type of mammal also pulled off this trick, and that’s the manatee. We haven’t looked at them yet, but they are slow animals as well, and have six neck bones. The very slow metabolisms of the manatee and the sloth may actually make them resistant to cancer and DNA damage, which would mean that when evolution gave their neck bones a slip, they survived the change and even though it didn’t necessarily confer any specific advantage or disadvantage, they passed it on to their kids with a shrug. A very slow shrug.

Sloths. So weird.

Sloth distribution.

9.1b – The Virginia Opossum

One opossum to rule them all. (Photo by Cody Pope)

Easily the most famous of all the opossums, the Virgina opossum is better known than all its relatives combined. When someone talks about an opossum, or even inaccurately about a plain old possum, they are almost certainly talking about the Virgina opossum. It is the only marsupial that lives in North America, found in about half of the United States and in most of Central America — and is expanding into new territory even as you read this.

A nocturnal creature with a grey body and a distinctive white face, it is the animal that gave the very name to opossums everywhere, since “opossum” is derived from a Native American word meaning “white animal”. It is the biggest of the opossums, the size of a housecat, and is a resourceful, solitary, successful creature.

As an opportunistic omnivore, the Virgina opossum can eat just about anything, including rotten fruit and human garbage, making them pests in human environments much like raccoons. But the Virginia opossum is not nearly as smart as a raccoon — despite its size, it has a very tiny brain and acts largely on instinct, including its involuntary death-faking response to extreme danger.

Which is important, because at the end of the day the animal has very little in the way of other defense mechanisms. It will hiss and bare its teeth and act in a very hostile manner, but it doesn’t really pose a danger to anything that wants to hurt it. All it can do is run away or hope that playing dead will save it. Because of their relatively defenseless nature, opossums don’t live long, and aren’t expected to. Even if it doesn’t get eaten, a Virginia opossum in the wild will only live about two years

Virginia opossums have 50 teeth, which is the most of any North American mammal, and they also have opposable thumbs, like humans and monkeys and such, allowing them to grasp and manipulate objects such as branches, fruit, and the lid of your garbage can. Like all opossums they have a prehensile tail for grasping and climbing. Yet with all this, perhaps their most interesting anatomical feature is that the females have within their pouches exactly 13 unlucky nipples, arranged in a perfect circle of 12 with one in the middle, like some sort of Lovecraftian opossum nipple monster.

"... what?" (Photo by Risssa)

The Virginia opossum was once found mostly in the American southeast, but during the Great Depression humans purposefully relocated large numbers of opossums into the midwest, the area hardest hit by the Depression, because they were easy to kill and made good eating, which would help the population. From there the opossums shrugged and kept going west, and are now found all along the Pacific coast of America. Back in the east they spread northward and are now common all along the eastern seaboard and as far west as Michigan and parts of Minnesota. They are now spreading into southern Canada. The most interesting part of this expansion is that the further north Virginia opossums go, the bigger they get, so that opossums in Michigan are noticeably larger than opossums in Texas. This appears to be some sort of fast-acting physiological response to the cold.

The most famous recent Virginia opossum lived in a German zoo. If you have ever seen the internet meme of a fake-looking opossum with fake-looking crossed eyes, well, it’s actually completely real. This was Heidi, a real-life cross-eyed Virginia opossum. Believe it or not, the eyes in the pictures were not Photoshopped. Heidi had a Facebook page with 290,000 followers, which is … a few more than mine. Unfortunately she was put down with health problems in September of 2011.

9 – The Book of Didelphimorphia

"Im-possum-ble!" (Photo by Tree & J. Hensdill)

Pronounced die-DEL-feh-MOR-fee-uh, this order is simply the opossums, no more and no less. When you think of an opossum, you probably think of the Virginia opossum, a grey-and-white beastie that lives in North and Central America and plays dead. Yet there are a hundred different species of opossums spread throughout the Americas, making them the second-largest order of marsupials.

That’s right, opossums are marsupials. Typically we associate the term marsupial with animals living in Australia, but Australia and South America were once connected, and there are still many marsupials living there who neglected to hop on board the island-continent express, some of which have moved up to Central America and even North America. The opossums have pouches and give birth to underdeveloped joeys just like the Australian animals.

Before we begin, it’s important to note that there is a difference between an opossum and a possum. Even though opossums are commonly called possums, they are actually two different types of animal. The possum is a different sort of marsupial, living in Australia, with a nicer disposition and no propensity to play dead. Why they were given such close names is anyone’s guess. It’s probably because scientists like it when we’re confused, so they can look smarter in comparison.

Opossums are found throughout South and Central America, with one, the Virginia opossum, found in much of the United States as well. The smallest opossum is only the size of a mouse, while the largest is as big as a nice, fat housecat. For the most part they will eat just about anything they can get their jaws around, from meat and carrion to insects, fruit, and garbage. They are found as often in trees as on the ground.

There are three very cool things about opossums.

One: opossums have a powerful immune system and many of them are impervious to snake venom. Like the mongoose, opossums will kill and eat snakes, but they are not as well-known for it. Their immune system has not however rendered them immune to rabies, but very few opossums carry the disease. If you lined up a hundred wild dogs and a hundred opossums and let them all bite you, you’d be dead or in a lot of pain, but chances are only the dogs would have given you rabies.

Two: opossums have a prehensile tail, which is one of the greatest things animals have ever developed and a fantastic argument in favour of radical human gene-alteration. A prehensile tail is a tail that can be controlled just like an arm. It can be moved around at will and can grasp objects. Their tails are not strong enough to let them dangle from branches with them, but they give the animal the advantage of a fifth limb when climbing.

(I’m just kidding about the gene alteration, but imagine the possibilities.)

Three: opossums can, as the saying goes, play possum. The phrase of course originates from them, and it means to fake death in order to make a predator lose interest. This works because many predators prefer to kill their own food when possible, and are less likely to be interested in what appears to be carrion.

Is it dead? No one knows, and no one wants to taste it to find out. (Photo by Johnruble)

When an opossum plays dead, it doesn’t just fall over and try to stay still. It goes all the way, and it actually doesn’t even have a choice. They don’t consciously choose to do it; it’s an automatic response when injured or in what they feel is an extremely threatening situation.

When things get bad enough to trigger the fake death response, an opossum’s lip will draw back to expose the teeth, saliva will bubble out, the eyes will partially close, the animal will fall down, an awful-smelling green liquid will run from its bottom to make it smell dead, and it will enter what is essentially a coma. You can’t call its bluff, because it’s not really bluffing. The opossum is completely out of it. Its eyes won’t move, and you can’t prod it back awake. You could pick up an opossum in this state and carry it around, and it still wouldn’t react or appear to be anything other than dead. You might actually be carrying a dead opossum.

They will stay in this unconscious, death-like state for at least 40 minutes, and sometimes as long as four hours. When coming back around its ears will start to twitch first. So if that opossum you’re carrying gets twitchy ears, look out.

The reason you should look out is because playing dead is not the opossum’s first response to danger. Unless it feels like it is in serious trouble, an opossum will first growl, hiss, and possibly bite with its sharp little teeth. Baby opossums often haven’t developed the fake-death response yet, and will simply hiss angrily until the threat goes away.

Opossum distribution

6.1a – The Nine-Banded Armadillo

Taking over America, one state at a time. (Photo by Mwcolgan8)

Several armadillos get their name from the number of bands they have, meaning the number of flexible leathery armour bands in the middle of their bodies, and the nine-banded armadillo has the highest number of any so-named. It is also, coincidentally, the most widespread armadillo, found from the middle of the United States all the way south to Argentina. They originated in South America but have been making their way north ever since the Americas joined together, three million years ago.

In fact, they are still doing so. Before the late 1800s, armadillos were not found in the United States, but then the nine-banded armadillos began to cross the Rio Grande and enter Texas. By 1995 they were fully established in many southern states. Getting the hang of this expansion thing, they then exploded further northward, and by 2005 were established as far north as Kansas. They are still pushing northward, with individuals spotted in Nebraska, Illinois, and Indiana. Can nothing stop the relentless march of the nine-banded armadillo?

Cold weather will do it, actually. Armadillos do not like cold winters, and are unlikely to reach as far north even as the Canadian border. But they are firmly entrenched in all the states they’ve entered so far, because they have no real natural predators in the United States, unlike in central and South America where they are hunted by the skull-crushing jaguar. In addition, humans don’t have any real interest in hunting and eating armadillos, what with the possibility of contracting leprosy and all.

So for the most part we leave them alone, except when they make pests of themselves by stealing eggs from farms, and for the most part they leave us alone, except when they want our delicious eggs. They give birth to four genetically identical babies every year, which means their populations grow quickly and in some areas people are worried that there are too many armadillos. They can be a hazard on highways because of their habit of jumping straight up into the path of oncoming vehicles instead of running away. This may seem suicidal, but it’s likely an evolutionary defense mechanism to scare away predators by surprising them. The cars are sure surprised all right. This habit of leaping in the path of speeding vehicles is the only thing stopping the USA from standing for the United States of Armadillos.

"Oh man, I'm going to jump right in front of this car. That'll scare it away. This is gonna be great." (Photo by Gigrantula)

When not stealing eggs, nine-banded armadillos typically eat insects such as termites or ants. To that end, they love to dig, and they do it well. Though they shamble along pretty slowly most of the time, they will run quickly from danger when they have to, and if they haven’t jumped into a car’s bumper first. Though they cannot roll themselves into a ball, they have a similar strategy that they sometimes employ, which is to dig a small, quick hole when threatened and wedge themselves into it with only their armoured back sticking out. At this point most predators will poke the creature a few times, try and fail to pry it out, and give up in disgust, muttering something about sour armadillos as they wander away.

5.2e – The Vampire Bat

He doesn't vant to suck your blood. He just vants to lick it a little. (Photo by Ltshears)

There are exactly three bats in the world that feed on blood, and they are the three species of vampire bat, found in central and South America. Lots of bats get a bad reputation because of the vampire bats, but only these three are parasites who live off the blood of living creatures.

Contrary to popular terminology, vampire bats do not “suck” blood out of anything. They use small, razor-sharp teeth to make tiny cuts in an animal’s skin, and then lick the blood that comes out.

One of the most interesting things about vampire bats is how they find sleeping animals and then choose where to make their incisions. Vampire bats have a specially developed sense of hearing that allows them to tell when an animal is breathing the deep, regular breaths of sleep and when the animal is awake. This is important, because sleeping animals are much less likely to notice the small, quick cut or the bat’s licking tongue. Once the bat has a likely target chosen, it uses wonderful thermoreceptors on its nose to find the warmest parts of the animal’s skin, which is where the blood flows closest to the surface. The vampire bats are the only mammals capable of naturally detecting infrared signals like this.

Vampire bats practice something known as social thermoregulation, which is a fancy term that means keeping warm by using friends. Vampire bat colonies can number in the thousands of bats, but within each colony there are smaller groups that roost together. When temperatures are warm, each of these groups will be smaller, and will tend to exclude males. When it gets colder, the groups get bigger, letting more males in as they roost together to keep warm.

But what you probably don’t know about vampire bats is just how helpful and kind they can be with each other. Yes, they are parasites of a sort, and yes, they live off blood instead of fruit or insects, and yes, they are kind of creepy, but they really aren’t so bad when you get to know them.

"I pay my taxes and mow my lawn like anyone else. What I do with your blood in the privacy of your own home is none of your business." (Photo by Acatenazzi)

For example, if a mother bat dies, another vampire bat will adopt any orphaned babies, looking after them, feeding them, and raising them as if they were her own. They are the only bats known to do this. In addition, vampire bats will share food. A vampire bat must feed on blood at least every two days or it is in danger of starving to death. If a bat can’t find food, it will beg for help from the other bats. Some of the other bats will helpfully regurgitate a little bit of their day’s blood food, so that the hungry bat can eat. They will also groom one another socially, much like primates.

Two of the three vampire bat species feed on the blood of birds, and only the third, the common vampire bat, will feed on mammals. They will feed on pretty much any sort of mammal, including humans, which is why we don’t like them. When spotting a target, the bat will land a short distance away and approach along the ground in a stealthy manner. Vampire bats are quite good at moving along the ground, and can “run” at speeds of up to 5 miles per hour, which is a fantastic image.

If the animal has hair, the vampire bat will actually use its sharp teeth to shave away a little patch to reveal the skin, which is quite clever. The bat’s saliva acts as an anticoagulant, which means that it stops the blood from clotting up and scabbing, so that the bat can feed longer from a single cut.

You aren’t in danger of having your blood drained by a vampire bat, as they only take about one fluid ounce of it before they are full and head off to digest your lovely blood. However there is always the chance they might give you rabies. About 0.5 percent of vampire bats carry rabies.

Humans, as we so often do, have fictionalized a lot of the attributes of vampire bats into the mythological idea of vampires. But real vampire bats are not evil. Blood is simply how they survive, and they do not take enough to do real harm so long as they don’t pass on rabies. All the same, it is understandable that we don’t like them. Anything that might feed on us while we sleep tends not to get a page in our good books. But beyond the whole blood thing, they are clever, social little creatures, and utterly unique.