A bit of curiosity, how can a vampire bat survive on blood alone?

Contrary to popular belief, vampire bats are not gigantic beasts out for human blood. On the contrary, most of them are up to 9 centimeters long, feed on the bloodstream of mammals much larger than themselves – but they do not take care of sucking all the blood.

Clearly surviving on blood alone can’t be easy, but a handful of genetic tweaks may have helped vampire bats evolve to become the only mammal known to feed exclusively on the stuff. These bats have evolved a variety of behavioral and physiological strategies to live on a blood-only diet, but 13 genes that bats appear to have lost over time could underpin some of the behavior.

These genes are associated with sweet and bitter taste receptors in other animals, meaning vampire bats likely have a diminished sense of taste, much better for drinking blood. The other 10 missing genes were recently identified in bats, and the researchers propose several ideas about how the absence of these genes might support a blood-rich diet.

Some of the genes help raise insulin levels in the body and convert ingested sugar into a form that can be stored. Given the low blood sugar, this processing and storage system may be less active in bats. vampires and genes are probably not that useful anymore. Another gene is involved in other mammals with the production of gastric acid, which helps break down solid food, and that gene may well have been lost as the vampire bat’s stomach evolved to store and absorb primarily liquids.

One of the other missing genes inhibits iron absorption in gastrointestinal cells. Blood is low in calories but rich in iron; vampire bats must drink up to 1.4 times their own weight during each meal, and in doing so, ingest a potentially harmful amount of iron. Gastrointestinal cells are shed regularly in the vampire bat’s gut, so by losing that gene, bats can absorb large amounts of iron and quickly excrete it to avoid overload, an idea supported by previous research.