Only three bat species truly live on blood meals
Desmodontinae leaf-nosed bats of Central and South America are the only mammals specialised for hematophagy—feeding on blood. Three living species, each in its own genus, look more like one another than like any other bat, suggesting the blood diet evolved once in a shared ancestor.
Only three living mammals feed on nothing but blood, and all are bats of Central and South America: the common vampire, the hairy-legged vampire and the white-winged vampire. Each sits in a genus of its own within Desmodontinae, a subfamily of the New World leaf-nosed bats, though older books gave them a separate family. Two extinct Desmodus species have been found in North America. The spectral bat, despite the Latin name Vampyrum, never drinks blood.
Because the three resemble each other more than any other bat, blood-feeding probably evolved just once. Their lineage split from relatives about 26 million years ago, and within some 4 million years had every adaptation it needed, one of the fastest bouts of natural selection known in mammals. Recent work points to insect-eating ancestors, and since the most basal species, the hairy-legged vampire, drinks bird blood, the first vampires may have too. The diet is hard to live on: huge fluid volumes, excess protein and the threat of iron overload. Vampires cope partly by losing the REP15 gene, which boosts iron secretion, and a common vampire starts urinating within two minutes of feeding.
The toolkit is precise. Thermoreceptors on the nose, built by tuning the heat channel TRPV1 to switch on at about 30 °C, locate blood near the skin. The bat walks up to a sleeping host on all fours, shaves fur with its cheek teeth, and slices a cut roughly 7 mm wide and 8 mm deep with enamel-free incisors that stay razor sharp. Saliva keeps blood flowing and vessels open, and a 40 g female can drink over 20 g in twenty minutes. They have also lost the receptors for sweet and umami tastes.
Colonies roost in dark caves, wells, hollow trees and buildings. A vampire can last only about two days without a meal, so a bat that comes back hungry begs, and a donor may regurgitate blood for it. Reciprocity predicts sharing better than kinship does. In the wild they live around nine years.
Source: Vampire bat
