ORDER: Chiroptera--Bats
SUBORDER: Microchiroptera--True Bats
SUPERFAMILY: Phyllostomoide

FAMILY: Phyllostomidae--New World leaf nosed bats
GENUS: Desmodontinae

Desmodus, Diaemus, Diphylla

 

   
 

I am often asked if all bats "suck" blood. In fact, there are no bats that "suck" blood. Only 3 species out of the almost 1000 bat species, are vampire bats. Vampires do not suck blood, they make a razor sharp wound in their prey; then lap blood from the wound.

Vampire bats are the most feared and misunderstood of all bats. The very mention of their name conjures up the vision of a large beast flying through an open bedroom window, puncturing the neck of a sleeping beauty, then sucking the life blood out of its unsuspecting victim.


In reality, there are no vampires (at least bats) anywhere in Europe or the United States. The three species of true vampire bats all reside in Mexico, Central America, and South America. They are tiny creatures, no larger than a mouse, with an average weight of around one-ounce (28.35 grams), and an average body length of 2.75" with an 8" wingspan (19.44 centimeters). They have no interest in the neck of a sleeping beauty, unless that sleeping beauty happens to be a cow. Vampires feed on cattle, other livestock, and birds. Vampires seldom bite dogs since dogs can hear sounds of higher frequency than larger mammals and would likely waken.

Originally, vampires fed on the blood of wild animals and the population of bats was held in check by the amount of food available. With the influx of domestic cattle into Latin America, they found an inexhaustible food supply and their numbers have increased dramatically.

The most studied and familiar of species, the common vampire bat Desmodus rotundus lives almost exclusively on mammal blood. The hairy-legged vampire Diphylla ecaudata feeds almost exclusively on bird blood, and the rare white-winged vampire Diaemus youngi prefers the blood of birds, but also feeds on the blood of mammals. The licking of blood by the Desmodus is the most thoroughly studied feeding behavior.

The common vampire bat is a crevice dweller, sometimes roosting alone, but most often in small colonies or in colonies of up to a thousand. Members of these colonies will recognize each other individually. Although there are some squabbles over territory, they do not use their sharp teeth in a fight.

The vampire prefers a roost of almost total darkness; caves, old wells, abandoned buildings, hollow trees, or mine shafts. They will sometimes move from one daytime roost to another, which is closer to their prey. This kind of activity indicates that they learn from experience where their prey can be found. Vampires use rivers as navigational tools as they move from one part of their range to another. The rivers are easier to follow than wooded routes, and cattle often graze in pastures near water.

Vampires leave their roost in after dark, often traveling in small groups of 2 - 6, flying just above the ground. They are most active around midnight. Vampires locate and recognize their hosts by smell, appearance, echolocation, radiated body heat, and breathing sounds. All bats are great fliers, but the vampire is also a great walker. They literally tiptoe up to their donor, jumping in all directions to avoid the movements of their host. They can jump like a frog, leap straight up into the air, or walk on two legs like a monkey!

They rarely waken the sleeping prey and their donor scarcely notices the painless bite. They feed on only one donor per night, do not bite deeply, nor do they struggle with their donor. It has been observed that a vampire visited the same donor on several consecutive nights, always opening the old wound. Often several animals can share a bite, since it takes a while for the wound to close due to anticoagulants that enter the wound from the bat's saliva. It has been observed that a wound has bled for as long as 8 hours.

The same enzymes in vampire bat saliva that keep a victim's blood flowing may soon be used to fight heart disease in humans. Scientists believe those anticoagulants will effectively dissolve human blood clots, the major cause of heart attacks.

A blood meal lasts about 25 minutes, although the entire process of locating prey and making the incision can take up to 2 hours. The wound the vampire makes is approximately 5 mm deep and 5 mm in diameter, and does not cut arteries or veins. If you made a wound this size on your body, it would produce about one drop of blood or less than a gram. Different sources quote the amount of blood ingested by a vampire to be between 5 and 8 teaspoons per night. This is a heavy weight for a one-ounce creature to carry on the flight back to the roost.  Because warmer ambient air temperature demands less energy expenditure, calculations have shown the net gain in energy through the intake of blood is possible only in the Tropics.

Because of their highly specialized food intake, vampire bats have had to adapt in many ways. Their mouth structure is different: they have fewer teeth than most bat species, the incisors and canines are shear-like, the cutting edge forming a "V" and all traces of crushing surfaces are absent. Other indications of their liquid diet include a tongue that is adapted to lapping, a short esophagus, and a slender stomach adapted to stretch to hold and digest blood. Their wings and body structure have adapted to taking off with a great load.

In addition, unlike some other bat species, vampires breed year round. After a long gestation period of seven months, they generally give birth to one youngster, on rare occasions, twins. The juvenile development of vampires is very slow in comparison with other bat species. They continue to be suckled up to nine months: the change from a milk diet to a blood diet being difficult. This suckling time is three months longer than the flying foxes, which are many times their size and at least six months longer than most other bats. Relatively early on the youngsters will lick small amounts of blood from the mouths of returning adults. In their fourth to fifth month, he youngster begins to accompany the mother while foraging. Again, unlike other bat species, motherless youngsters are not doomed to starve. Other females will adopt them.

Since vampires do not accumulate large fat reserves, they cannot survive more than two or three days without a meal. Vampires reduce the danger of starvation through their impressive altruistic behavior. In response to a specific pattern of begging behavior engaged in by animals that have failed to obtain a meal, vampires will regurgitate part of their meal to help another!

Considering their complex anatomical and physiological specialization, and their amazing social structure, vampires are surely among the most fascinating of bats.

   
 

Literature Cited:

The Biology of Bats, Gerhard Neuweiler, Oxford Press, 2000
Eyes on Nature/Bats, Celia Bland, Kidsbooks, Inc., 1997
Walker's Bats of the World, Ronald M. Nowak, Johns Hopkins University Press, 1994
The World of Bats, Klaus Richarz & Alfred Limbrunner, TFH Publications, Inc., 1993
Bats, M. Brock Fenton, Facts on File, 1992

 
 
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