Vampire Bats: Do They Really Drink Blood?

Read time: 5 min

The short answer: yes!

Vampire bats do indeed consume blood, hence the name – but these are not the evil winged creatures that popular culture would have us believe. Vampire bats are actually very interesting animals, and although they have become synonymous with Hallowe’en, nightmares, and all things that go bump in the night, these tropical mammals are really an example of clever evolutionary adaptations.

Bats are really fascinating creatures. They are the only mammals that can fly, but vampire bats are most impressive of all: for they are the only known mammalian sanguivores (‘sanguivore’ is the scientific name given to a creature that survives by ingesting blood). So, they’re very unique – but hardly the mysterious ghouls known to folklore. Just like other mammals, young vampire bats are dependent upon their mothers’ milk and will cling tightly to her body for about three months before moving to an adult diet.

How many bat species drink blood?

There are more than 1,400 bat species in the world, and only 3 of these drink blood: the common vampire bat Desmodus rotundus, the hairy-legged vampire bat Diphylla ecaudata, and the white-winged vampire bat Diaemus youngi, all of which are native to the tropics of Mexico, South America and Central America. Many people may not even know that more than one species of vampire bat exists, but most of us will be familiar with the common vampire bat. This is possibly due to the more memorable name, but more probably because this bat tends to feed on the blood of other mammals like cows, pigs, dogs, horses (and even occasionally humans), more so than the other two species – which instead prefer feeding on birds like sleeping chickens. It’s easy to see how superstitious myths could develop! For the most part, the common vampire bat tends to feed on livestock, but can feed on almost any type of animal – according to vampire bat scientist Gerald Carter, they bite porcupines, snakes, sea lions, armadillos, even penguins. Human bites are very rare, and if they do occur most people won’t even know they’ve been fed on: vampire bats only consume about a tablespoon of blood.

When and how do they feed?

Vampire bats will only hunt when it is dark, and actively search for animals that are sleeping. One vampire bat drinks between 15 – 25ml in one blood meal, and will die within 3 days if they fail to acquire any blood. Vampire bats are also one of the few animals that could be said to practice reciprocal altruism; starving bats will fly back to the roost and beg for food from other bats, who will regurgitate blood. This regurgitation is thought to come at a high cost to the giver.

What’s really interesting is that the common vampire bat doesn’t swoop down from above, as you might imagine: instead, it approaches the target from below. The bat lands first, and approaches the chosen animal on the ground – moving on all fours – before targeting an ankle or crawling up a leg. Then, using thermoception via a heat sensor in its nose, it locates a spot where warm blood is flowing just under the skins surface. After biting an artery with specially developed teeth, a protein (appropriately called Draculin!) in the bat’s saliva acts as an anticoagulant, preventing any blood clots and allowing the bat to drink its fill. Vampire bats are unobtrusive, and can feed on another animal for over 30 minutes without being noticed. What’s important to remember is that the bats don’t actually suck any blood out – after cutting a small crater-shaped groove with their razer sharp incisor teeth, a vampire bat will let it bleed and dip in their long tongue, lapping up the blood like a cat through two lateral grooves in the tongue – kind of like a specially developed straw.

Why do they drink blood?

All three of these vampire bat species have evolved from fruit-eating ancestors – scientists think they made the shift towards consuming blood millions of years ago, but still aren’t entirely sure how they made the huge leap to a food source of relatively low nutrition. Blood is a tricky diet to survive on alone. Consisting of almost 80% water, blood is very low in nutrients – and of the small proportion it does have, 93% are proteins. Digesting this is very hard on the kidneys, not to mention the dangers which accompany hematophagy: like risk of blood-borne disease and a range of pathogens, as well as effects such as iron poisoning. (‘Hematophagy’ is the scientific name for the practice of consuming blood).

Up until recently, it has been a mystery how vampire bats survive on a diet of blood alone. However, a 2018 study  found that distinct gut bacteria are key to the vampire bat’s ability to survive on blood, and that over 280 bacterial species found in vampire bats are known to cause disease in other mammals.  The study also found that the vampire bat’s genome had more ‘transposons’ (or ‘jumping genes’). Very generally speaking, these are elements in a DNA sequence that can ‘jump’ around within a genome, creating and reversing mutations and altering the cell’s genetic ID. The research found that one in particular, called MULE-MuDR, was 2.2 times more present in the common vampire bat’s genome than in other fruit-eating bats. Scientists think that this could be a key part of how the bats are able to process huge amounts of blood without getting sick.

“The data suggests that there is a close evolutionary relationship between the gut microbiome and the genome of the vampire bat for adaptation to sanguivory (feeding exclusively on blood),” 

Marie Zepeda Mendoza, Biologist

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