Gut Bacteria Key to the Vampire Bat’s Ability to Survive on Blood

Only three mammalian species are sanguivorous—that’s blood feeding—and they are all bats. Blood, apparently, is not that nutritious. It has almost no carbs, fats, or vitamins; its high iron levels can disrupt heart, liver, and pancreas function; its obscenely high protein and salt levels can cause renal disease if nitrogenous waste products build up.

It contains pathogens. It clots.

Source: arstechnica.com