October 17, 2021

I, Science

The science magazine of Imperial College

“Again I woke in the night, and found Lucy sitting up in bed, still asleep, pointing to the window…between me and the moonlight flitted a great bat, coming and going in great, whirling circles.” (Dracula, p104).

Vampire bats have been flitting around human imaginations for a while. Unused to thinking of ourselves as a food source, the idea of a mammal that wants to drink our blood is hideously creepy. But how does reality compare to the myths?

There are three kinds of Vampire bats on our planet and none of them live in Transylvania. The Common Vampire Bat, the Hairy-legged Vampire Bat and the White-Winged Vampire Bat all live in Central and South America. Dracula’s home is in reality more likely to be a disused mine shaft than a gothic castle.

Even more disappointing (or more perhaps reassuring) is that the bats don’t specialise in feeding on humans. Out of the three species only the Common Bat is a pure mammal specialist and even they actually prefer cows.

It is true that blood is their only food source. Their bodies can’t physically process any other kind of food. They track down their meals by: appearance, smell, echolocation, body heat and breathing sounds. With the help of specialised thermoreceptors on their nose they can even locate where the blood is flowing closest to the skin and land on just the right place.

Here is where it gets really interesting; Vampire bats don’t always land on their food sources if they think it could wake them up. Instead they can creep up on them slowly. This can happen because Vampire bats don’t just fly; they can also walk on the ground.

Even better than that, they can run:

It might be worth remembering after that that vampire bats are actually only around two and half inches long. That’s about the size of a mouse so you can put the pitchforks away now. When it comes to biting, bats are also discreet; the cuts are only 5mm deep and will, in most cases, not even be felt by the sleeping animal.

Vampire bats unusual are also one of zoology’s favourite examples of cooperative altruism. They are the only known bat species that will feed the young of other bats and will even nurse orphaned bats with their own. Their blood drinking lifestyle is a risky business and strong social bonds ensure that young bats can survive even if the mother dies.

This type of altruistic behaviour continues among adult bats as well. Bats that do not feed within 48 hours will die but finding a blood meal every night is not a guarantee. Successful bats will therefore regurgitate blood for their starving neighbours. When the tables are reversed, the bats will then take their turn to feed the hungry bats who helped them. It is the pressures from feeding on blood that have helped lead to this cooperative behaviour and strong social bonds.

So there you have it, the night flying, blood drinking, altruistic Vampire bat. Take that Dracula