How Bloodsucking Vampire Bats Aim Their Bites

Let's say you're a vampire bat, and you are trying to decide where to bite your victim. You want a spot rich in blood, right? But how do you find such a spot?

Turns out, vampire bats have a kind of remote sensing ability that can tell them where there is a warm patch of skin on a nearby animal. A warm patch of skin means there are blood vessels just below the skin surface. And now scientists have identified the molecular basis for this remote sensing ability.

"Vampire bats need to get about 2 tablespoons ... of blood a day," says Brock Fenton, a bat biologist at the University of Western Ontario. "If they're not successful, they can make it through one day without feeding, but they can't make it through two days. So the vampire bat that came home last night without having fed, if he doesn't get something to eat tonight, he's going to be dead."

This puts a huge pressure on these animals to be able to find blood donors.

"They really have evolved some amazing features, I think, that fit in with this bloodthirsty lifestyle," says David Julius, a molecular biologist at the University of California, San Francisco. Julius got interested in vampire bats as an outgrowth of his work on the molecular basis of pain.

One kind of pain we've all experienced is burning pain. There is a particular kind of molecule that's essential for our heat sensation called a TRP receptor. These TRP receptors don't just respond to hot heat — they also respond to the heat we get from biting into a red-hot chili pepper.

"From a nerve-endings standpoint and a molecular standpoint, they're quite similar," he says. "I think we perceive them as being different because we recognize the difference between touching something hot and eating a hot chili pepper or getting the oil from chili pepper in our eye or in our fingers."

So what's this got to do with vampire bats? Vampire bats have these same heat-sensing TRP receptors, but they use them differently. As Julius reports in the journal Nature, bats have nerve cells on their faces that have a particular form of these TRP receptors, and they can detect temperature from a distance. In practical terms, this means they can sense a warm patch of skin on a nearby animal. And where there is warmer skin, there are lots of blood vessels near the skin surface, giving the bat a good idea where to bite.

Pit Vipers, Too

And it's not just bats that have the ability to sense heat from a distance. Pit vipers can do it, too.

"You can cover the eyes of the snake and the snake looks out on the world and literally sees the world in heat," says Michael Grace of the Florida Institute of Technology. It forms an image of the thermal environment in the brain. And this image is accurate enough for a snake to bite its prey.

So if you come across a rattlesnake wearing a blindfold, don't think you're safe.

There's one other thing Julius has learned about vampire bats. "Most people look at a bat and they presume that it's closely related to rodents," he says, and that's what most scientists used to think. But recently, some biologists have concluded that bats are more closely related to a grouping of animals that includes moles, cows and horses. Julius has compared the DNA sequence of the TRP receptors in bats with the sequence in moles and cows and horses.

"And our data suggest that bats are most closely related to those animals," says Julius.

So don't think of bats as flying rodents — think of them as itty bitty flying horses. Maybe that will make them seem more lovable.

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