The common vampire bat (Desmodus rotundus) is one of the most widely known and misunderstood species of bat. They are in the suborder Microchiroptera, the family Phyllostomidae, and the subfamily Desmodontinae. (Nowak, 1994) The common vampire bat has no tail, has a head and body length of about 70-90 mm and a forearm length of 50-63 mm. Adults usually weigh between 15-50 grams and have pointed ears and a long thumb. (Nowak, 1994) Vampire bats walk around on all fours more than most bats, and have developed strong legs for jumping and walking. (Economist, 1996) Their fur is short and grayish-brown with a silvery sheen. (Graham, 1994) They are found from Mexico to Chile and Argentina as well as the islands of Margarita and Trinidad. (Nowak, 1994) Vampire bats are one of the few species that have benefited from the clearing of forests for farmland; previously uncommon, they have increased in number due to the increased access to livestock in formerly forested areas. (Yusada, 2004)
Vampire bats roost in hollow trees or caves, either alone, in small groups of 20 to 100, or large colonies consisting of over 2000 individuals. (Nowak, 1994) In cases where a large number of bats are residing together, the bats can often be divided into smaller stable social groups consisting of 8-20 females and their young, presided over by a single adult male. Other males live in groups nearby and frequently try to replace the top male. Generally, breeding occurs year-round, and some females produce more than one litter a year. (Nowak, 1994) After a gestation period of around 210 days, the female gives birth to a single well-developed young. (Nowak, 1994) Females nurse the young until 2months of age, when they begin regurgitating blood for them, and young bats start foraging for blood themselves around 4 months of age. Young bats are completely weaned around 9-10 months of age, around the same time that sexual maturity is reached. (Nowak, 1994) There has been some discussion on whether or not vampire bats exhibit altruistic behavior. Vampire bats have been known to regurgitate blood for a starving bat who begs for food. (Weisburd, 1984) However, studies have shown that the bats who regurgitate food for starving bats are likely to do so only if the starving bat is kin or a ³friend²- a regular roostmate who is likely to reciprocate the behavior at a later time. (Altringham, 1996) Vampire bats therefore show signs of both kin-selection a reciprocal altruism, with laboratory experiments showing that the tightest reciprocal sharing occurred between pairs of bats. (Altringham, 1996)
Vampire bats are by far best-known for their feeding habits. Unlike other species of bat, vampire bats feed solely on blood from other animals. Desmodus rotundus primarily feeds on the blood of large livestock animals like cows and horses. (Altringham, 1996) The vampire batıs anatomy is specially designed for this habit. Its noseleaf contains heat sensors for locating capillaries under the skin and the canine teeth are modified to allow the bat to clip off feathers or fur. (Altringham, 1996) Its sharp incisors can open a wound without the host animal feeling it, and its grooved tongue expedites the flow of blood into the batıs mouth. (Altringham, 1996) The vampire batıs saliva contains an anticoagulant called desmoteplase to keep the blood flowing smoothly without clotting. (Cheater, 2003) A bat may consume 60% of its weight (20-25mL) in blood during a single meal, which can make a return to the roost impossible. Since only the red blood cells contain nutritional value, the batıs specialized stomach and kidneys rapidly remove the plasma, often while the bat is still feeding, to minimize weight gain. (Altringham, 1996)
The actual feeding habits of vampire bats is a stark contrast to the popular legends of vampire bats which seek out humans, bite them on the neck and suck their blood. Vampire bats prefer to feed from livestock, and they lick up blood rather than sucking it out. In fact, the bite of a vampire bat may be more beneficial to humans than it is harmful. Researchers have investigated the use of the anticoagulant in vampire batsı saliva to treat stroke victims. The anti-clotting enzyme used in the studies is referred to as Desmodus rotundus salivary plasminogen activator (DSPA). This enzyme destroys fibrin, the protein that binds blood cells together and causes a clot. (Current Science, 2003) Mice were injected with chemicals to cause the same type of stroke-clots that frequently occur in humans. Then some mice were injected with DSPA while others received tissue plasminogen activator (tPA), the standard drug used to break up clots. (Seppa, 2003) tPA is known to cause neuron damage or brain bleeding and is only effective within 3 hours of the stroke, after which point the negative side effects outweigh the benefits. DSPA caused less than 1% as much neuron damage as tPA, and was effective up to 9 hours after the stroke. (Seppa, 2003) Although more studies are needed, DSPA from vampire bats could save the lives of many stroke victims.
A more realistic factor that gives vampire bats a bad image is rabies. Not only can vampire bats transmit rabies to livestock and humans, but also the wounds inflicted by vampire bats are prone to screwfly infestations. (Graham, 1994) In Latin America, the number of cattle lost to rabies spread by vampire bats is estimated to be around 100,000 animals per year, at a value of about $48 million. (Meltzer, 1998) Vampire bats can also contribute to the loss of cattle due to blood loss or infection of the bite wound. The resulting sickness of the cattle can lead to weight loss and decreased milk production, and possibly death if secondary parasites cause further infection of the wound. (Meltzer, 1998) Human deaths from vampire bat-spread rabies are extremely rare, although two cases were reported in September 2001 in Costa Rica. (Badilla, 2003) It is believed in these two cases that rabies was not spread directly to the victims from a vampire bat, but rather a cat that was infected with rabies from a vampire bat had bitten the victims.
Vampire bats are a highly misunderstood species of bat. Though they are depicted as bloodthirsty human-hunters by legend, they are in fact non-aggressive creatures that take care of their young and roostmates and consume relatively small amounts of blood from their hosts. The danger to humans from vampire-bat-spread rabies is greatly overestimated, especially in comparison to the potential benefits that vampire bat anticoagulants can bestow on stroke victims. Perhaps with a better understanding of vampire bats, people will begin to accept and respect vampire bats instead of fear them.
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Erin Kolski