Cattleman Francisco Oliva was on a roundup -- of vampire bats. After a swarm of the blood-slurping creatures dive-bombed his herd and drank their fill one recent night, he corralled several dozen in special contraptions that look like giant badminton nets.

He put each bat in a cage and then applied a poison called vampirin to their backs with a brush before releasing them. Back in their roost, the animals would be groomed by as many as 20 other bats, causing their deaths. Or so Oliva hoped.

"We have to look for answers, because this little animal is very stubborn," Oliva said days after the capture, surveying his 300-head herd, most of them bearing bat-fang markings and red stains from the nightly bloodletting. Oliva said he would exterminate every single bat if he could.

"You keep the good and get rid of the bad," said the rancher, philosophical but weary from the nocturnal attacks that have reached Transylvanian proportions of late, "and these little beasts are terrible."

More than 100 miles away, on an island research station in the middle of the Panama Canal, Stefan M. Klose begged to differ. He not only stuck up for Desmodus rotundus, the scientific name for the most common vampire bat, but described the animals as boons to humanity. Bat-based research has led to the development of sonar and anti-coagulant medicines that prevent heart attacks, he pointed out, and scientists are only beginning to understand the creatures.

"I certainly defend vampire bats' right to a place in the ecosystem," said Klose, a German zoologist who does fieldwork at the Barro Colorado tropical scientific center run by the Smithsonian Institution. People's irrational reaction to vampires, he said, reflects "our primal fear of being someone else's food object."

Klose also confessed a fondness for the creatures. The scientist said feeding time, when the bats accept bits of banana from his hand, is a "really sweet and peaceful sight. It always reminds me of how close these animals are to us and how incredibly intelligent they are -- certainly more exotic and wilder than my neighbor's dog, but no less smart or cuddly."

Few animals inspire the repugnance and fascination of vampire bats, and perhaps nowhere are opinions more divided than in Panama, with 120 bat species. Bats are found globally except in Antarctica, but thrive in the tropical rain forests that cover much of Panama because of plentiful animal and plant foods, abundant shelter and the warm climate. In a tropical environment's biodiversity, bats "have more niches to exploit," Klose said.

On one side of the debate are farmers such as Oliva who are suffering from an escalating plague; on the other are scientists who use bats and the scientific breakthroughs they have inspired to promote biodiversity.

"Bats have developed a radar system that can distinguish the tiniest insect in the middle of dense bush in the dead of night," said Todd Capson, a Smithsonian staff scientist who tracks the development of technology derived from tropical flora and fauna. "It's inconceivable there isn't something more to learn from that."

But the benefits of bats are a tough sell here. Sabine Spehn, another German researcher who recently did fieldwork in Panama, said by telephone from the German city of Ulm that her efforts to explain "the nice things about bats" to Panamanians, such as insect control and seed and pollen dispersion, came to naught.

"The response I got was always, 'The only good bat is a dead bat,' " Spehn said.

Oliva can be forgiven for feeling antagonistic. Here in Panama's remote and hilly south, he and other cattlemen wage a continual battle against a variety of livestock pests such as coyotes, crocodiles, ticks and worms, and a host of tropical diseases. But he has been driven to the edge of desperation by the increasing bat attacks.

Though vampire bats have long been present in Panama, their attacks have ebbed and flowed. "But now the bad cycles have become more frequent," said Argis Barrios, president of Panama's National Cattlemen's Association. Scientists theorize that timber cutting has flushed bats out of food-rich forests as cattle herds have grown, providing a ready-made and usually stationary food supply for the bats. "The problem is a man-made one," Spehn said.

During the month of April alone, Oliva said, he lost 10 calves to anemia caused by successive bloodlettings. He and other cattlemen bemoan the scarcity of the bat-catching nets, which are strictly controlled by the Panamanian government to prevent their use to capture endangered birds.

Good bats -- that is, the non-vampires -- make up the overwhelming majority of the 1,100 known bat species. Even the scariest of the lot, the greater flying fox of New Guinea, a bat with a Dracula-like wingspan of more than five feet, preys on only jungle fruit and insects. There are just three blood-sucking, or vampire, species of bats.

"The problem is, there are many bats, many cattlemen and very few nets," Oliva said as he examined his pockmarked cattle. Several of his surviving calves had a desiccated look and were weak and unsteady on their feet from anemia.

Oliva said adult vampire bats, which have a wingspan of eight inches, swoop down by the hundreds over his herd, land on the ground and then jump up on the animals' legs, underbellies or faces to bite them. A bat's saliva contains an anticoagulant that makes blood flow freely, and the bat laps up the blood with its tongue.

While sympathetic to the ranchers, Klose says further study of bats might yield more breakthroughs.

"Who would have thought reef sponges could lead to anti-cancer drugs, that the scales of butterfly wings could help bring about better kinds of paint? But they are being studied for it," Klose said. "In fact, very little of what we have invented has been made from scratch. Nature usually provides the template.

"Vampires could hold the key to a problem we want to solve, like AIDS or cancer. But if you destroy them, they are lost for eternity."

Zoologist Stefan Klose holds a fruit bat at Smithsonian Tropical Research Institute on Barro Colorado island in Panama. He calls bats "certainly more exotic and wilder" than most pet dogs but "no less smart or cuddly."