10/30/2020

Vampire Bats Just Want To Be Friends

17:22 minutes

a bat lands upside down on the ceiling
A lot of unique maneuvers are needed for bats to land upside down. Watch the aerodynamics of bat flight in a SciFri Macroscope video! Credit: Breuer and Sharon Swartz

It’s almost Halloween, which means it’s time to get a little spooky. A perfect time for the newest installment of our Charismatic Creature Corner!

This month, we’re diving into the wild world of vampire bats. These little mammals are native to Central and South America, and have bodies about the size of a mouse. 

A vampire bat hanging from a wall of its cave
Should the vampire bat earn the coveted charismatic creature title? Credit: Shutterstock

And yes, let’s address the elephant in the room: Vampire bats have a diet that consists entirely of blood. They gravitate toward livestock, but have been known to feed on people too. Their status as blood-suckers makes them one of the only mammals classified as parasites.

Despite their gruesome diets, vampire bats are extremely social creatures, and are known to display acts of friendships with other bats. In fact, a study last year found that vampire bat friendships forged in captivity actually last when the bats are released into the wild. Friendships are important for vampire bats: They result in food sharing, which is integral to keeping everyone fed and happy.

Science Friday’s Charismatic Creature Correspondent, producer Kathleen Davis, is back to convince Ira that this creature is worthy of entry into the Charismatic Creature Corner Hall of Fame. Joining them is Dan Riskin, an evolutionary biologist and adjunct professor of biology at the University of Toronto, Mississauga.


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Segment Guests

Dan Riskin

Dan Riskin is an adjunct professor of Biology at the University of Toronto, Mississauga in Toronto, Canada.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. It’s time for another Charismatic Creature Corner. This time we’re getting a little spooky.

[MUSIC PLAYING, NOCTURNAL INSECT NOISES]

[CAWING]

[LION’S ROAR]

[CREEPY LAUGHTER]

Yeah. Joining me again is our Charismatic Creature Correspondent– that’s not her making those noises– SciFri producer, Kathleen Davis. Hi, Kathleen.

KATHLEEN DAVIS: Hey, Ira.

IRA FLATOW: Remind our listeners about our Charismatic Creature Corner.

KATHLEEN DAVIS: Right, so this is the segment where I bring you a creature, and with the help of a guest, we try to convince you that this creature is worthy of being inducted into our Charismatic Creature Hall of Fame. So that means it’s worthy of sitting among more traditionally charismatic creatures like red pandas or sloths, you may say.

IRA FLATOW: Yeah right, now I get it.

KATHLEEN DAVIS: And as you might remember, we don’t make it easy for ourselves. In the past, we have talked about hell ants, as well as slime molds.

IRA FLATOW: Charismatic both. I can only imagine what creature you’ve brought us this time.

KATHLEEN DAVIS: Well, it is the day before Halloween, so of course, we have to get a little bit spooky. Ira, what do you think about vampire bats?

IRA FLATOW: Well, you know, I once visited a scientist known as the bat lady of Barnard, who fed her vampire bats frozen blood from an ice cube tray in her freezer. But I’m yet to be convinced they are charismatic.

KATHLEEN DAVIS: Well, I think they’re great. And I am here to convince you that they are, with the help of a special guest. We’ve got Dr. Dan Riskin, an evolutionary biologist, currently an adjunct professor of biology at the University of Toronto Mississauga. Welcome to Science Friday, Dan.

DAN RISKIN: Thanks for having me.

KATHLEEN DAVIS: I think to start, before we get into why vampire bats are so cool and cute, we need to get the obvious out of the way. Vampire bats drink blood, right?

DAN RISKIN: Yeah, they do. To be honest, that’s part of what makes them so charismatic. But they’re weird among mammals because they have become parasites. So they are a group of three bats that are only found in the Americas. And they have adapted to feeding on the blood of other animals, and getting all their calories that way, which is super weird for a mammal to do. And as a result of that, they’ve also changed in other weird ways, and become totally different from other mammals.

IRA FLATOW: Can you give us a little verbal picture? How big are they? Where can you find them?

DAN RISKIN: So vampire bats are a lot smaller than people expect. They’re actually just little things– about the size of a mouse, frankly. The wingspan is only about 18 centimeters. So like, seven inches. And they’re almost nothing when you see them on the wall. They’re just little balls of fur.

So there are three kinds of vampire bats. The one that’s best studied is the common vampire bat. That’s the one that you hear about most. They feed on cattle mostly. But there are also two others– the white-winged vampire bat, and the hairy-legged vampire bat. Now, those two are bird specialists.

So in all three cases, these bats, they sneak up on a sleeping animal in the nighttime, and they make a little tiny cut. Somewhere inconspicuous, like maybe the toe of a sleeping bird, or maybe near the ear of a sleeping cow, or near it’s hoof. And then they put their jaw up against that little new wound.

They’ve just made a tiny cut. And they start licking. And they lick, and they drink, and they pee. And they sit there for up to 20 minutes, getting their fill. And then when they’re full, they leave and they go back to the roost and digest it. But they have a very tight budget, so they have to be able to do this pretty much every single night.

IRA FLATOW: You’re trying to convince me this is charismatic. So far, that description is sort of blood-curdling, more than anything else.

DAN RISKIN: Well no, if the blood curdles, they starve. And so, that’s part of the game. They have to have a way to keep that blood flowing. And so their saliva has special chemicals in it to keep the blood from clotting. Because it’s honestly, if you take a common vampire bat that feeds on mammals and sometimes does feed on people, that cut is only about half a centimeter deep, half a centimeter wide. And it would clot relatively quickly if left to its own devices.

So the bat has to keep licking and drinking. It’s not sucking on it. It doesn’t have its fangs stabbed into the skin. It’s just licking and drinking. And that saliva has all these chemical properties that keep it flowing. And the saliva becomes very interesting, because now you’ve got something that stops clotting from happening. And there are all kinds of drugs that have been inspired by bat saliva– just trying to figure out how to do that medically.

IRA FLATOW: Well, now you’ve got me into the “that’s a really cool thing” kind of idea. That is cool. But what kinds of animals do they prefer? Do they like one kind over another?

DAN RISKIN: So one of the great mysteries with these bats is what their native food was, because if you take a common vampire bat, they love feeding on cattle. And cattle– it’s like we brought McDonald’s drive-throughs into the Americas for the bats to feed on, because there were no cows there back in the day. It was 1493, I think, that the first cow came over. And so now they’re totally adopted to feeding on cattle. But we don’t know what they were feeding on before. It’s an open question.

So anytime a vampire bat is seen feeding on some native animal in the Americas, like a tapir or anything else– or a person, for that matter– everybody gets all excited, because this might be a hint about what they were doing before. And there is the possibility– there were a lot of people in the Americas before the Europeans came over. They were huge societies. And it’s quite possible that for vampire bats, for a long time, people were their main source of food. We don’t have proof of that, but it’s a respectable hypothesis.

IRA FLATOW: Do we know why they evolved to just drink blood? It seems like such an odd evolutionary pathway.

DAN RISKIN: It’s a real question, about how you end up worked into that corner. And in an evolutionary sense of feeding on blood, because once you’re feeding on blood it’s really hard to get fat, because there isn’t a lot of fat in blood. And so when you’re drinking, you can sort of satisfy your needs. But once the blood runs out, once your stomach’s empty, you don’t have a big budget to get going again.

And so there’s a big problem for bats. If they can’t get food pretty much every single night, this causes a huge problem for them. But they’ve come up with a solution, which is to share. And so vampire bats are famous in the biology world, because if you come home after failing to find a cow to feed on, your buddies, even if they’re not related to you, will often vomit in your mouth for you. Which is just– what better way to show that you love someone than to do that? And vampire bats will do this for each other. And as a result, the whole colony can, kind of, get by when a few of them aren’t able to find food.

And there are all kinds of studies about who barfs for whom. And if you barfed for me last week, so I got your back this time. But hey, you held out last time, when I was asking you, so forget it. I’m not going to help you out this time All of these social dynamics all play out, and they have to be very intelligent to keep track of who is sharing and who’s trying to cheat. And they do. They keep track of it all. And as a result, they’re very intelligent animals.

KATHLEEN DAVIS: So would it be fair to say that vampire bats have friends?

DAN RISKIN: Yes, it would definitely be fair to say vampire bats have friends. In fact, there’s a study that just came out this year that showed that when bats were kept in a captive colony, and made friends with their buddies, after they were released and allowed to go into a huge colony of vampire bats in a great big tree in Panama, and able to just disperse and make new friends, they kind of stuck with their buddies from high school. They had friends already, and that’s who they chose to stick with after they went there. And so these friendships are long term. And friendship sounds like a non-scientific word, but really it’s kind of the best word for it.

IRA FLATOW: Dan, you’re kind of famous in the bat research world for a particular study you did a little while back, where you put vampire bats on a treadmill.

DAN RISKIN: Yes, that is my absolute claim to fame. I’m the guy that put vampire bats on a treadmill. And to be honest, I didn’t know it was going to go as well as it did. But so I was a young PhD student, and I knew that they were good on the ground, at walking and crawling and stuff like that. So I just wanted to see how they walk, and I wanted to compare it to other animals.

And the way all the other animals are studied– horse, cat, dog, whatever– you put it on a treadmill, you change the speed, and you look at how it’s leg movements change. And so that seemed easy enough. So I built this box with a floor that moved. It was like a little plexiglass breadbox. And so we went to Trinidad, we caught some vampire bats, we put them into this box, one at a time.

And I turned it on, and the bat started walking. And they’re walking gait was beautiful. It was exactly like a cat, exactly like a dog, but a little bit lower center of mass, a little bit creepy. Kind of like the movie of Bram Stoker’s Dracula, when Gary Oldman is going up the wall. It was pretty much exactly that. That gait.

But they could do this over a whole range of speeds, and so I wanted to know what the upper limit was to how fast they could walk. And so we cranked the speed a little bit, and this one bat switched from walking to these running push-ups. So all of a sudden it was bounding into the air, pushing off with its wings, and then landing on its hind limbs, and then pushing off with its wings again, in a gait that had never been seen before. And so I was shocked.

I tested another bat. It did the same thing. Another bat, another bat, another bat– and lo and behold, we had discovered that these vampire bats have a running gait that doesn’t exist in any other animal. So bats as a lineage have generally become very bad at walking. But the vampire bats, with their feeding on blood and sneaking up on animals, have evolved a new running gait. And so we discovered that. That was my– it still is. It’s a highlight for sure. I’m so proud of that.

KATHLEEN DAVIS: Dan, as somebody who has studied vampire bats for a while now, have you ever been bitten by one?

DAN RISKIN: Well, I had a close call. I haven’t been fed on by vampire bats, thankfully. What I keep telling the people I’m working with is, relax, there’s cows nearby. They really do prefer cows over people. It’s much easier to get blood out of a cow than to get blood out of a person.

In some of the places I go, it’s quite common for the cattle to get fed on by vampire bats. And I have been lucky that way. But I did once catch a vampire bat in a mist net. So mist nets are the way you catch birds or bats. And we’d set one up. And the vampire bats, you almost always catch them on the bottom layer.

That’s the neat thing about vampires, they fly really close to the ground. Or maybe they’re running a little bit, too. We don’t exactly know. And so we caught this vampire bat. And I grabbed it with my big thick glove. And the gloves were just too thick. I couldn’t untangle it. So I took one glove off, and I was working to get the vampire bat out, and it quickly turned its head and hit the tip of my finger. And I pulled back, and I expected to be bleeding, but I was not. And I thought, oh, that was close. I thought it hit me, but it didn’t.

And I finished getting the bat out. And we got it back into the big cage where we were going to keep it. And then a little later, I realized I had a big flap of skin on the tip of my finger that had been sliced. So it was such a sharp cut that I didn’t even feel it. But it basically cut the callus off the tip of my finger I wasn’t bleeding, but it was a good reminder of what they can do with those teeth.

IRA FLATOW: Wow. Speaking of which, if vampire bats are living on blood, how come they don’t get sick from whatever sickness these animals may be having in their blood?

DAN RISKIN: They do get sick. And so there are diseases that can spread from wildlife to vampire bats. And there are problems with different diseases that can spread. And rabies is one disease that can spread to vampire bats. And that becomes a huge problem because then it spreads to other livestock.

But the disease moves differently in different animals. And this is something that’s getting a ton of attention right now with COVID-19, because it’s thought that that disease probably came from bats originally. And so there’s a whole bunch of coronaviruses, for example– not to mention other viruses, like Ebola– that come from bats.

And the bats don’t show the same kinds of symptoms as people do when they get these things. And so there’s a lot of research into the immune systems of bats, to try to understand how it is that those diseases that are so deadly for us, how the bats do so well with those diseases, in spite of them.

But yeah, vampire bats do get sick sometimes. And what’s really interesting is the way they deal with being sick. So there’s a study that came out just this week showing that when vampire bats get sick, they tend to socially isolate. They tend to stay away from the friends they had. These researchers put transmitters on them. They can tell how far apart they are from other transmitters. And so all the bats in the colony– or a bunch of them– are wearing these things, and they know exactly how close the bats get to each other.

And when they experimentally made some of the bats feel a little bit unwell for a couple of days, but the bats were fine in the end– those bats that weren’t feeling well tended to be withdrawn. They didn’t mix with the other bats. They stayed away from them. They did exactly what Anthony Fauci says you’re supposed to do– they socially isolated. And then when they felt better they went back to it. And so studying how bats deal with illness is another place where vampire bats are just a treasure trove of information that can be useful to us.

IRA FLATOW: I’m Ira Flatow. This is Science Friday, from WNYC Studios. We’re talking with the bat fanatic, I have to call him. He’s a bat biologist– Dan Riskin, who is at the University of Toronto Mississauga. Dan, is there anything that you don’t know about these bats, or any bats, that you still need to know?

DAN RISKIN: Yeah, I mean, everything. That’s a beauty of any kind of scientific system is the more you learn, the more you want to know. And the more questions you have. And for me, one of the really interesting questions that I literally lie awake at night thinking about has to do with echolocation.

So echolocation is something that most people have a pretty good grip on. It’s this idea that a bat shouts, and then hears the echo. And the difference between the noise it made and the noise it hears, along with the amount of time it took, tells them something about how far away things are, and what they’re going after, so they can avoid flying into trees. And even more impressively, they could pick out a moth and then chase it down and catch it.

What people don’t realize, first of all, is that most of these bats are doing it extremely loudly. Some of these bats are as loud as smoke detectors. So if they were on a frequency we could hear, if they were low enough that we could hear them, they would be annoying as all get out. So it’s nice that they’re at these high-pitched noises we can’t figure out.

But here’s the thing. If you have one bat flying in one room, and there’s one moth, and it’s using its echoes to find that moth, I get it. I can kind of picture how that works. But put me in a cave with 10,000 bats all echolocating at the same time, flying in a giant cloud, how on god’s green earth do they know which one is their echo? How did they possibly hear their faint echo when the bat right next to them is screaming at the top of their lungs?

So for me, that is just a system that I just– people are working on it, and people understand pieces of it, but I just don’t– I can’t get my head around how that happens. Just go into a bat cave. It just fills you with this wonder of, like, we don’t know. We’ve barely scratched the surface on understanding these beautiful creatures, and how they live their lives.

KATHLEEN DAVIS: So bats are, at least in my opinion, very cute. But people are still scared of them. That seems to be a common fear still for people. Are people justified in this fear?

DAN RISKIN: My experience has been that the fear of bats is a thing that’s changing. It used to be that if you looked up bat in an encyclopedia, you would find the one picture of a bat. And it was a picture someone had taken while they were holding it badly, and it was showing its teeth in self-defense. And it was sort of black and white and grainy. And it said some things about bats and how they fly, and they’re the only mammals that fly, and we just didn’t have that much to tell.

But now with the internet and with pictures and with videos, and with high-speed cameras and with good echolocation recordings, you can get an introduction to bats now that is much more interesting, and much more just fun to look at and engaging. And when I talk to kids about bats now, I never get this, eww, bats. I always get a, yay, bats. Kids love bats. And adults, for the most part, once they get the proper introduction, love them too.

And so I lead wildlife tours, sometimes, to different parts of the world. And I took a group to Borneo. And everybody was excited to see orangutans. And we did see orangutans. And the orangutans were great. But we also caught some bats while we were there, because I brought a net and I got permission. And when we caught those bats– these little things, these little pipistrelles– it was just magic.

I mean, you get to see them close up. You get to see what– they look right at you. And you get to see what the wing looks like. And you get to just see them still, not flying around your head, not in the dark. Just a nice introduction to them. And you get to see how cute and just vulnerable and adorable they are, and then you sort of start to contemplate how many different kinds there are, and all the different places you can go see them. And all the secrets they’re holding. And they’re just amazing. So I think the fear really comes down to just needing a better introduction to them

KATHLEEN DAVIS: Well, I think that Dan has laid out a fantastic case for the induction of the vampire bat to the Charismatic Creature Corner Hall of Fame. What do you think, Ira?

IRA FLATOW: Well, I was going to say that because of Dracula and people’s fear of bats, and whatever, that they are not charismatic. But Dan has turned me around.

DAN RISKIN: Sweet.

IRA FLATOW: Of all the– they are so talented and skillful. I never knew these things. So I’m going to say yes, they do belong in our Charismatic Creature Corner.

KATHLEEN DAVIS: Dan, are you satisfied with that answer?

DAN RISKIN: Well, yes. We should get to work on some other weird creatures. I’d love to see you do some more parasites, for sure.

KATHLEEN DAVIS: Thank you so much, Dan. Dan Riskin, an evolutionary biologist, currently an adjunct professor of biology at the University of Toronto Mississauga. Thanks Dan.

DAN RISKIN: Thank you.

IRA FLATOW: And thank you, Charismatic Creature Corner Correspondent, SciFri producer Kathleen Davis.

KATHLEEN DAVIS: Anytime, Ira.

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About Kathleen Davis

Kathleen Davis is an assistant producer at Science Friday, which means she spends the week brainstorming, researching, and writing, typically in that order. She’s a big fan of stories related to strange animal facts and dystopian technology.

About Ira Flatow

Ira Flatow is the host and executive producer of Science FridayHis green thumb has revived many an office plant at death’s door.

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