They can't bark, fetch or roll over, but the kennel full of "artificial dogs" at Cornell University makes a better home for fleas than any mutt could.

Fashioned from a glass feeder, a stack of sieves and a plastic membrane that passes for a skin, the fake pups were developed by veterinary researchers looking for a way to raise fleas in a controlled environment.

"It's more complicated than you might think to raise fleas for scientific purposes," said Susan E. Wade, a veterinary parasitologist at Cornell's College of Veterinary Medicine.

"They are almost impossible to keep track of on living animals, and their eggs fall off on the floor. We wanted to create something as similar as possible to a dog, where we can study fleas and retrieve them afterward."

Wade and her colleagues have now raised thousands of fleas, the first time several generations have been kept in an artificial environment.

The researchers fill the fake dogs with real blood, warming them to the 37 degrees Celsius needed to attract the fleas. When the fleas get hungry they move to the mesh of the upper sieve, pierce the membrane with their mouths and drink the blood.

Their eggs fall into the lower sieve where they are collected and counted.

Now that the scientists have raised several generations of the pesky insects, they are on the verge of a number of experiments, all dedicated to the proposition that the world could live happily with fewer fleas.

They are trying to find which chemicals work best to control them and what part of animal blood is essential for their nutrition. They are also trying to determine how fleas manage to reproduce so fast. In a warm, moist summer they can go from eggs to adults in two weeks.

The scientists have already learned at least one important new fact about the agile, wingless insects: Although they are famous for jumping hundreds of times their height, they would much rather walk.

"When fleas spend all their time hopping, they do not feed and they die of starvation and exhaustion," Wade said.