Why are vampire bats the only bats to seek blood?

There are several species of vampire bat in the world, and they’ve been found to be the only known mammals to solely survive by drinking the blood of other animals. The reason vampire bats can survive this way is that – unlike their fruit- and insect-eating cousins – their gut microbes work differently to digest blood, along with a built-in resistance to bloodborne viruses. Their DNA has also hardwired their kidney function to tolerate the high-protein intake that comes with a blood-only diet.

Vampire bats have to continually feed on blood, as missing just two meals could cause them to starve