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They love to suck blood, and scientists now know why!

The vampire bat is famous for inspiring the creation of Count Dracula and now scientists have found out why they are the only mammals that can survive on a diet of just blood.

It turns out they're missing loads of genes normally found in bats. The scientists worked it out by comparing vampire bat genes to 26 other living bat species.

And scientists also studied how they've also worked out how to work together to feed - and sometime share the blood between them - by regurgitating it - or sicking it up!

Over the years, the vampire bats have evolved to shed certain characteristics in order to better adapt to a diet of blood, which contains loads of iron and protein but not many fats or carbohydrates.

For example, three of the lost genes are responsible for taste that tell different foods apart, which doesn't matter if you only feast on blood.

According to the report in the journal Science Advances, this diet makes the vampire bat a very spooky and unusual animal.

These bats live in South and Central America and have a wingspan of seven inches. They survive by sucking blood from livestock or other animals at night.

Most mammals can't survive on a diet of blood and that includes most bat species too. Only three out of 1400 species of bats drink blood.

However, the vampire bats are very sophisticated mammals which rely on cooperation to make up for their poor diet.

According to researchers, the bats have to feed very regularly to get enough food to keep them going and commonly share regurgitated blood with roost mates that haven't been able to find a nightly meal.