It begins as a slow creep. One wingtip is placed in front of the other—left, right, left, right. Slowly, methodically, the vampire bat inches across the ground toward the sleeping tapir.
Vampire bats can stalk prey many thousands of times their own size, so one wrong move can mean a lost chance at a meal or worse, a hoof to the skull. Blood-feeding requires the stealth of a snow leopard, not the rash aerial acrobatics of the vampire bat’s insect-catching cousins. And so the vampire crawls.
From a distance of six inches, special sensors in the bat’s nose allow it to use infrared radiation to detect the heat of blood close to the skin. The only other animals with this superpower are few snakes like the pit vipers.
Once it zeroes in a hot spot, the vampire bat uses scalpel-like incisors to carve tiny divots in the tapir’s flesh. The bite is so fast and clean, the tapir doesn’t even stir in its slumber. An anticoagulant in the bat’s saliva (appropriately named draculin) causes the blood to flow freely. As the crickets and cicadas hum into the night, the vampire bat licks its lips and prepares to suck the lifeblood from another mammal.
But here’s where all the vampire lore gets it wrong. True vampires do not suck blood. They lick it.
“When they feed, I think they look rather more like a cute cat lapping up milk,” says Gerald Carter, a postdoctoral researcher at the Smithsonian Tropical Research Institute.
Whether it’s the lapping or the loping, there’s clearly a lot about the vampire bats that popular depictions like Bram Stoker’s Dracula and Vampire Bats (the made-for-TV movie) get wrong. Which is a shame, because vampire locomotion is fascinating—and their creeping is almost as creepy as the whole blood-licking business.
“Unlike other bats, [vampires] can walk, jump, and even run on the ground,” says Carter, who studies these animals in Panama.
What’s interesting here is that there are more than 1,300 known species of bats in the world. And precisely one of them is able to run. That’d be Desmodus rotundus, or the common vampire bat. We know this because of Dan Riskin.
Riskin is a man of many talents. He’s a respected bat expert, an adjunct professor at the University of Toronto Mississauga, and cohost of Discovery Channel’s Canadian science show Daily Planet. But he’s also the guy who put vampire bats on treadmills. I probably should have led with that.
Riskin has spent a great deal of time studying bat biomechanics on the ground. Most bat species do not do well under such circumstances. They are awkward and slow, easy pickings for a predator.
But where the others look like a fish out of water, the vampire is able to gallop like a spider-bunny.
By coaxing vampires onto tiny treadmills, Riskin found that the flying mammals could run at speeds of nearly 4.5 miles an hour. He suspects that they might be able to summon nearly twice that speed in a pinch. Like maybe if OK Go needed extras for a new music video.
“I think [the vampire gait] is a nice reminder that we move the way we do because of physical laws of stability and power, but also because of our evolutionary history,” says Riskin.
For example, squirrels and frogs developed a bounding gait because they were already on an evolutionary path guided by powerful hind limbs. Bats went in the opposite direction, giving up lower limb strength in exchange for powerful breast and arm muscles to command their wings. But then the vampire bat started to double back on that path.
“Vampires had the motor up front,” says Riskin, “so when they evolved a bounding gait it was forelimb-driven.”
This front wheel drive, as he refers to it, makes the vampire bat’s running stride “kinematically different from that of any other tetrapod.”
Other bat species do many more interesting things with their webby wings.
Bats in the genus Tadarida use their wings to swim. The Cheiromeles and Mystacinidae bats have slots on their sides that they can tuck their wings into to keep them out of the way when they’re resting or crawling. Bats of the Saccopteryx genus have little fanny-pack pockets on their wings, which scientists believe are used by the males to store urine, glandular secretions, and Mentos—everything you need to woo a lady bat.
Some bats use their wing as a sling to catch their babies as they’re born. Other species’ wings have blood vessels built to dilate when the bats need to cool off.
Bat biologists have identified more than 60 different ways bats use their wings besides flying. These include defense, hiding, courtship, grasping, grooming, and fanning. For instance, says Carter, most people don’t realize that bats catch insects in the air using their wings as nets.
There’s even a bat with suction cups built into its wings. It’s called Spix’s disk-winged bat (Thyroptera tricolor), it lives inside tents made of waxy leaves, and Holy Halloween, Batman, it’s my new favorite animal.
Clearly, we all could all stand to spend a little more time around these wonderful, wingèd beasts. Thanks to a partnership with the Organization for Bat Conservation, Carter has set up a citizen science project that allows you to watch a captive population of vampire bats and log what you see. He calls it Vampcam, and after spending way too much time there one night, I can tell you it is all kinds of addictive.
Stick around long enough and you might just see a bat take a buddy under its wing and regurgitate a blood meal—which is basically the fun-size Snickers of the vampire bat world. Trick or treat!
In memory of bat expert Michael J. “Mick” Harvey, who this summer was called to the great roost in the sky.