The question of whether bats drink blood is common, and the answer is a qualified yes. Out of the over 1,400 bat species worldwide, only three have evolved the unique trait of hematophagy, or feeding exclusively on blood. This highly specialized diet is extremely rare, making the widespread cultural myth of the blood-sucking bat a significant exaggeration.
The Three Species of Vampire Bats
The three species that practice hematophagy are the Common Vampire Bat (Desmodus rotundus), the Hairy-legged Vampire Bat (Diphylla ecaudata), and the White-winged Vampire Bat (Diaemus youngi). These are the only mammals known to survive entirely on blood, a diet that presents unique metabolic and digestive challenges. All three are restricted to the New World, inhabiting warm, humid climates across Central and South America, from Mexico down to parts of Argentina and Chile.
The Common Vampire Bat is the most abundant and well-studied, typically feeding on the blood of mammals, primarily livestock such as cattle and horses. The Hairy-legged and White-winged Vampire Bats mainly prey on birds. These bats are small, generally weighing less than two ounces, with a wingspan of about 12 to 15 inches.
The Mechanics of Blood Feeding
The popular image of a bat “sucking” blood is inaccurate; vampire bats actually lap up their meal. A bat approaches a sleeping host stealthily on the ground, using specialized heat sensors on its nose to locate an area where blood flows close to the skin’s surface. The bat then uses its razor-sharp upper incisor teeth to make a precise, shallow incision, creating a small wound.
The flow of blood is maintained by the bat’s saliva, which contains a cocktail of biochemical agents. The most famous is Draculin, a glycoprotein that acts as a potent anticoagulant by inhibiting coagulation factors IXa and Xa in the host’s blood. The saliva also contains a mild anesthetic to ensure the bite is painless, allowing the bat to feed for up to 30 minutes undetected. The bat’s grooved tongue then laps the flowing blood from the wound, consuming about two tablespoons in a single feeding.
The Diverse Diets of Non-Vampire Bats
The vast majority of bat species do not consume blood, and their diets are highly diverse, playing significant roles in their ecosystems. The largest group consists of insectivores, which feed primarily on insects. These bats, like the Little Brown Bat and the Big Brown Bat, consume enormous quantities of nocturnal pests, providing a natural form of pest control that benefits agriculture.
Other species focus on plant matter. Frugivorous bats, or fruit-eaters, disperse seeds over wide areas, a process that helps regenerate forests and maintain biodiversity. Nectivorous bats, which feed on nectar and pollen, act as important pollinators for various plants, including commercially valuable crops. These varied eating habits underscore that bats are far more beneficial than they are menacing.
Assessing the Health Risks
The primary health concern associated with bats is their potential to transmit the rabies virus, which is fatal if left untreated. While any mammal, including raccoons and skunks, can carry rabies, bats are the most common source of human rabies cases in the Americas. However, the percentage of bats that carry the virus is very low, often less than 0.5% in a healthy population.
Transmission to humans requires direct contact, such as a bite or scratch, or exposure to the bat’s saliva on an open wound or mucous membrane. The risk increases if a bat is found behaving strangely, such as flying during the day or being easily approached on the ground, which indicates illness. To minimize risk, people should never handle a bat and should seek immediate medical attention if contact occurs, as post-exposure prophylaxis is highly effective. Within the native range of vampire bats, there is also a risk of rabies transmission to domestic livestock, which is the main reason for local control efforts.