Common Vampire Bat

The common vampire bat is a small, ground-agile bat from Latin America that has taken up the strangest diet of any mammal: nothing but blood. Everything about it — its teeth, its saliva, its senses, even its social life — is shaped by the demands and risks of living on a food that spoils fast and runs out overnight.

Overview

Common vampire bats roost by day in caves, hollow trees, old wells, and buildings, in colonies of a few dozen to a few thousand, and fly out after dark to find a warm-blooded animal to feed on. They were historically limited by the availability of large wild mammals, but the spread of cattle ranching across the Americas has given them an almost unlimited food supply, and their range and numbers have grown accordingly.

Feeding on blood

Blood is an odd food — very high in protein and water, very low in fat and carbohydrate, and only available in small amounts before the host wakes. The vampire bat is built around these constraints:

• Teeth. The upper incisors and canines are large, triangular, and kept surgically sharp, with no enamel on the back edge so they self-hone. The bite removes a tiny divot of skin, and it is shallow and quick enough that a sleeping animal usually does not stir.
• Saliva. It contains anticoagulants — including a protein nicknamed draculin — plus compounds that keep blood vessels open and numb the wound, so the blood keeps flowing throughout the meal. A clot-busting drug developed from this saliva, desmoteplase, was tested as a stroke treatment.
• Heat sensing. Pit organs around the nose detect infrared radiation, letting the bat “see” where blood flows closest to the skin and choose the best spot to bite.
• Kidneys and gut. During the meal the bat rapidly urinates out the water in the blood so it is light enough to fly; back at the roost it slowly processes the concentrated protein.

Agile on the ground

Most bats are helpless on a flat surface. The vampire bat is the opposite: with powerful thumbs and legs it walks, sidles, jumps, and runs, using its wings like arms. It lands away from its target, closes in on foot, climbs aboard, feeds, and can launch back into flight even with a stomach-load of blood.

Sharing and society

Because a vampire bat can starve in two or three nights, an unlucky forager is in serious trouble. Roost-mates buffer this by regurgitating blood to bats that missed out. This sharing is not random — bats favour partners that have helped them before and with whom they have built a relationship through mutual grooming, one of the clearest known examples of reciprocal cooperation in a non-primate. Females often stay in their birth colony for life, forming stable, long-term groups.

Status and conflict

The common vampire bat is Least Concern and increasing. It is, however, the main wildlife source of rabies in Latin America, and bat-transmitted rabies in cattle causes substantial livestock losses, prompting control programmes. Poorly targeted culling — including cave burning and poisons — often kills large numbers of harmless, ecologically valuable fruit- and insect-eating bats, and is now discouraged in favour of livestock vaccination and selective methods.