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Science / Medicine : Vampire Bats : Creature That Inspired Dracula Tales Found Not to Deserve Vile Image; Bat Studies May Aid Man

August 26, 1991|SY MONTGOMERY | Montgomery is a free - lance writer based in Hancock, N.H

MONTEVERDE, COSTA RICA — It's probably the most loathed mammal on the planet.

Although only a few inches long, with the fewest teeth of any bat species, the common vampire--the Latin American blood-eater that inspired the 1899 tale of Dracula--arouses more horror and hatred than any other creature in the animal kingdom except, perhaps, snakes.

But the vampire's true life story, new research shows, is far more intriguing than the myths it inspires. As it turns out, the vampire is really--well, a very nice animal.

A recent field study reveals that the vampire does something that Dracula's author never suspected of such an "ignoble" animal: It shares blood meals with roost mates in need, a very rare and sophisticated form of altruism.

Even vampires' gruesome feeding preferences may well have a silver lining. Medical researchers now believe that an anti-clotting substance in the bat's saliva might lead to a new heart drug that could be used to save human lives.

"There are a lot of ironies about vampire bats," said Paul Robertson, Bat Conservation International's director of special projects. "The reality of the animal is completely different from almost everything people believe."

Even though the common vampire does live exclusively on blood, the little bat is no monster. Rather, the vampire is the Gandhi of carnivores: The bat doesn't kill its prey, and most of the time doesn't even hurt it. The vampire mostly obtains blood meals from cattle and horses--animals 10,000 times its size that don't miss the stolen blood. A sleeping cow won't even wake at the bat's quick, shallow bite.

The vampire is also generous: "Vampire bats have evolved a system of food exchange" in which they share blood meals with hungry roost mates, Gerald Wilkinson, a University of Maryland biologist, reports. "Only a few species--wild dogs, hyenas, chimpanzees and humans--are known to display such behavior," says Wilkinson.

For five years, Wilkinson spent two to six hours a day lying on his back, with his head thrust inside the opening at the base of a hollow tree, peering upward at roosting vampire bats in Costa Rica. From this uncomfortable position, he observed hungry bats begging food from vampires that had returned the night before as blood-bloated as carnivorous tennis balls.

The beggar would approach, lick under the round bat's wings, then the lips. If the request was honored, the donor would cloak the recipient with its wing, and then regurgitate blood directly into its mouth--all this accomplished as both bats were hanging upside down.

From hundreds of hours of watching more than 600 individually banded vampires, Wilkinson saw a pattern. Females fed blood to their own young, which was no surprise. But adult females also fed other "favorite" adult females, who would often return the favor. These individuals were not always genetically related. Instead, they were, as Wilkinson puts it, "friends" who tended to share roosts. Their friendships may last throughout the vampire's lifetime of about 18 years.

"Vampire bats are extremely intelligent, and really social animals," the researcher said. "Marvelous little animals."

If you still aren't impressed, consider this: One day a vampire might save lives.

Far from the hollow-tree bat roosts of Costa Rica, scientists at Merck, Sharp & Dohme Research Laboratories in West Point, Pa., are investigating how vampires' feeding methods could protect human hearts.

A vampire's saliva is more than ordinary bat drool. It's a virtual medicine chest: A natural anesthetic keeps the prey from even noticing the bite, and an anti-coagulant keeps blood flowing from the prey for up to six hours--enabling several vampires, one at a time, to lap leisurely at the wound for up to 30 minutes each over the course of the night. (One study, conducted in Costa Rica in the 1970s, found that because several bats can feed sequentially from a single wound, a colony of 100 bats may need bite only 3 cows in one night.)

Blood clots don't just threaten to spoil vampires' dinners; they also cause heart attacks in humans, when the clot blocks flow to the heart. This is what led Merck to search for anti- clotting agents--and to look at bat saliva. And it turns out, according to Merck scientist Stephen Gardell, bat saliva is 20 times more powerful than any anti-clotting substance manufactured to date. Bat saliva could, he said, could "prove more effective than anything now available" for breaking up clots that cause heart attacks.

Anti-clotting agents now available (including aspirin and Genentech Inc.'s Activase) have another drawback: They may cause unwanted bleeding. Scientists think this may not be a problem with vampire saliva because one of the proteins isolated from the secretion becomes active only when it encounters a clot.

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