vampire bat

 

name for the blood-drinking bats of the family Desmodontidae, found in the New World tropics. Vampire bats feed exclusively on the blood of living animals and are thus the only true parasites among mammals. There are three species ranging from Argentina to N Mexico. They are small (about 3 in./7.5 cm long), round-bodied bats with large, pointed ears and naked snouts. Unlike most bats, vampire bats can walk on all fours with the body lifted off the ground; it is in this manner that they approach their sleeping prey. The bat uses its razor-sharp incisors to make a neat incision, usually without waking the victim, then laps the blood with its tongue. Its saliva contains an anticoagulant that causes the wound to seep for several hours. Vampire bats parasitize a variety of animals, chiefly mammals. Although the quantity of blood they take is insufficent to harm a large animal, they are dangerous to livestock and humans because they transmit serious diseases such as rabies and Chagas's disease. Vampire bats live in caves, tree hollows, and houses. They are mutual groomers, and an effective method of reducing their numbers is to coat a captured bat with a sticky poison and release it; when the bat returns to its roost the poison will be licked by other bats. Members of another bat family, the Megadermatidae, of the Old World tropics, are known as false vampire bats. They are exclusively carnivorous but do not feed on blood. The generic name Vampyrus belongs to a large, fruit-eating bat of Central and South America that was once mistakenly believed to suck blood. True vampire bats are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Chiroptera, family Desmodontidae.

For the 1933 movie, see The Vampire Bat.

Vampire bats
Common Vampire Bat, Desmodus rotundus
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Chiroptera Family: Phyllostomidae Subfamily: Desmodontinae
Genera
Desmodus Diphylla Diaemus

Vampire bats are bats that feed on blood (hematophagy). There are only three bat species that feed on blood: The Common Vampire Bat (Desmodus rotundus), the Hairy-legged Vampire Bat (Diphylla ecaudata), and the White-winged Vampire Bat (Diaemus youngi). All three species are native to the Americas, ranging from Mexico to Brazil, Chile, and Argentina.

Species

The three species are quite different from each other, and are therefore placed within different genera (no other species are currently classified in any of the three genera concerned). But they are related. In older literature, the three genera are placed within a family, Desmodontidae, but this is now regarded as unhelpful, as it hides the similarities the vampire bats have with other members of the American leaf-nosed bat family, Phyllostomidae.

They are therefore now grouped as a subfamily, the Desmodontinae within the Phyllostomidae. The fact that the three known species of vampire bat all seem more similar to one another than to any other species suggests that sanguivorous habits (feeding on blood) only evolved once, and that all three species share a common ancestor.

Anatomy

Unlike fruit-eating bats, the vampire bat has a short, conical muzzle. It also lacks a nose leaf, instead having naked pads with U-shaped grooves at the tip. The common vampire bat also has specialised infrared sensors on its nose (see [1]), which aids them in locating an area where the blood flows close to the skin. A nucleus has been found in the brain of vampire bats that has a similar position and has similar histology to the infrared nucleus of infrared sensitive snakes.

They have small ears and a short tail membrane. Their front teeth are specialised for cutting and their back teeth are much smaller than in other bats. Their digestive systems are also specialised for their liquid diet. The saliva of vampire bats contains a substance, draculin, which prevents the victim's blood from clotting. They, therefore, lap blood rather than suck it as most people imagine.

The inferior coliculus, part of the bat's brain that processes sound, is specialized for detecting the regular breathing sounds of a sleeping animal such as a cow.

Feeding

Vampire bats hunt only when it is fully dark. Like fruit-eating bats, and unlike insectivorous and fish-eating bats, they only emit low-energy sound pulses. The Common Vampire Bat feeds mostly on the blood of mammals. whereas the Hairy-legged Vampire Bat, and the White-winged Vampire Bat feed on the blood of birds. Once the common vampire bat locates a host, usually a sleeping mammal, they land and approach it on the ground. They are very agile and a recent study found that common vampire bats can, in addition to walk, run at speeds of up to 2.2 meters per second. They possibly locate a suitable place to bite using their infrared sensors.

If there is fur on the skin, the Common Vampire Bat uses its canine and cheek teeth like a barber's shears to clip away the hairs. The bat's razor-sharp upper incisor teeth then make a 7mm long and 8mm deep cut. The upper incisors lack enamel, making it easier to keep them razor sharp.

The bat’s saliva is a key element in feeding from the wound. While grooves on the underside of the tongue draw blood toward the bat's mouth, the saliva has several ingredients that prolong bleeding. One is an anticoagulant that counters the clotting defenses. A second keeps red blood cells from sticking together and a third inhibits the constriction of veins near the wound.

Digestion

A typical vampire bat weighs 40 grams yet will consume over 20 grams (1 fluid ounces) of blood in a 20-minute feed. This feeding pattern adds another degree of complexity to its anatomy. They feed entirely on blood. Ordinarily this volume of food would make flight after a feeding session impossible. However, the bat has an amazing ability to rapidly process and digest the blood.

The stomach lining rapidly absorbs the blood plasma. In turn, the circulatory system shunts the plasma to the kidneys. From there it passes to the bladder and out of the bat. Within two minutes of beginning to feed, a Common Vampire Bat begins to expel highly dilute urine containing the plasma (which has no nutritive value).

While shedding the plasma makes taking off from the ground easier, the bat still has added almost 20-30% of its body weight in blood. To take off from the ground the bat must generate extra lift which it does by crouching and flinging itself in the air. Typically within two hours of setting out, the Common Vampire Bat returns to its roost and settles down to spend the rest of the night digesting its blood meal. However, when the bat is resting, a new problem is faced. The large protein intake creates excess urea and must also be disposed of. The urinary system of the vampire bat then uses various hormones to make concentrated urine -- consisting of more urea and less water.

Habitats

Vampire bats tend to live in colonies in almost completely dark places, such as caves, old wells, hollow trees, and buildings. Colonies can range from a single individual to thousands. They often roost with other species of bat. They will almost always have only one offspring per breeding season. Each colony will typically contain only one reproducing male, with around twenty females and their offspring. They need blood at least once every few days to survive. If they can't get blood, they'll approach another vampire bat whilst roosting, asking for a blood 'transfusion'. The blood is exchanged mouth-to-mouth in a motion that looks very much like kissing. Vampire bats can live up to nine years in the wild and up to 19 in captivity.

Role in the spread of disease

Vampire bats are common carriers of the deadly rabies virus which, aside from its danger to humans, is responsible for the deaths of many thousands of farm animals each year in tropical and sub-tropical America.

The unique properties of vampire bats do, however, also have some positive value in medicine. A study which appeared in the January 10, 2003 issue of , tested a genetically engineered drug called desmoteplase, which uses the anticoagulant properties of the saliva of Desmodus rotundus, and was shown to increase blood flow in stroke patients.

References

• Greenhall, Arthur M. 1961. Bats in Agriculture. A Ministry of Agriculture Publication. Trinidad and Tobago.
• Greenhall, Arthur M. 1965. The Feeding Habits of Trinidad Vampire Bats.
• Greenhall, A., G. Joermann, U. Schmidt, M. Seidel. 1983. Mammalian Species: Desmodus rotundus. American Society of Mammalogists, 202: 1-6.
• A.M. Greenhall and U. Schmidt, editors. 1988. Natural History of Vampire Bats, CRC Press, Boca Raton, Florida. ISBN 0849367506; ISBN 978-0849367502
• Riskin, Daniel K. and John W. Hermanson. 2005. Biomechanics: Independent evolution of running in vampire bats. Nature 434: 292-292. Abstract, video.
• Kishida R, Goris RC, Terashima S, Dubbeldam JL. (1984) A suspected infrared-recipient nucleus in the brainstem of the vampire bat, Desmodus rotundus. Brain Res. 322:351-5.
• Campbell A, Naik RR, Sowards L, Stone MO. (2002) Biological infrared imaging and sensing. Micron 33:211-225. pdf.

External links

• Schutt, W.A., Jr. "Dark Banquet" a website devoted to the biology of blood feeding creatures.
• Vampires: The Real Story - about the vampire bat.

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