Scientists Solve Mystery of How Vampire Bats Feed on Blood Without Becoming Sick

Why vampire bats eat blood and how they manage to do so without becoming sick has long been a source of mystery. Drinking blood doesn't make much sense from a nutritional standpoint, and the substance is typically rife with viruses and bacteria. But now scientists have a better understanding of how common vampire bats can live off the stuff.

Very few animals could live off of blood as a primary food source. In addition to containing pathogens, blood—though full of iron, nitrogen and salt—has very little carbohydrate or vitamin value.

So how do common vampire bats survive on hematophagy, or sanguivory, as the practice of eating blood is called? New research published in the journal Nature Ecology and Evolution says that the answer lies in their guts and genes.

A vampire bat at the Cincinnati Zoo laps up blood. For most creatures, this diet would be deadly. Mark Dumont / Flickr

The genome of a vampire bat contains twice as many transposable elements as the genome of other bat species. Transposable elements are pieces of genetic code that can move from place to place. Biologists studying the bats noticed that these transposable elements were found in regions that work with the immune system and metabolism. That's not surprising because you'd need to have a strong immune system to survive off a substance that carries so many viruses.

The researchers found that these genes also help the flying mammals to process the high levels of nitrogen and iron in blood that would be toxic to other animals.

Furthermore, common vampire bats have a special microbiome in their guts that lets them digest blood. Their stomachs are filled with hundreds of different types of bacteria that protect them from the diseases in blood. In other animals, these bacteria would harm their hosts, so it's especially surprising that these bats can carry them.

This study can't answer exactly how these bats learned to drink blood when so many of their relatives eat meat, fruit, or insects. But co-author Tom Gilbert, a geneticist at the Natural History Museum of Denmark, suspects that vampire bats may have begun the transition from eating insects to blood by eating blood-filled insects like mosquitoes.

Bats are particularly odd mammals. Roughly a quarter of all known mammal species are bats, and for their size, they are exceptionally long-lived. They are also vital to ecosystems because they eat insects and pollinate fruit. Although contact with bats sometimes leads to rabies, in general having them around is a good thing for human health (which is why collectors of bat mummies may want to reconsider their hobby).