In August and September in Washington, people who otherwise embrace natural foods and organic gardening can be found basting their households with pesticides, desperate to wipe out fleas.

Every year about this time the fleas begin emerging -- as hard to escape as the 17-year cicadas that littered Washington earlier this summer, but with none of the cicada charm.

It looks as if the flea infestation "is going to be very heavy," said Debby Goble, office manager of Friendship Hospital for Animals. "There are already indications from the month of July, when it was heavier than at the same time last year."

"It's a banner year for insects," said Sally Love, director of the Smithsonian's Insect Zoo. "Sometimes weather conditions are better for different types of population outbreaks, but it could also be that people's awareness of insects was heightened by the cicadas ... "

Unlike the cicada novelty, where opinion was divided between people fascinated by the creatures and those appalled by them, there is little good to say about fleas. They come in multiple varieties, one of which is credited with spreading the bubonic plague.

The principal pest among fleas in the United States is the cat flea, which also democratically infests dogs, according to Richard S. Patterson, research leader of the fly and household insect section of the U.S. Department of Agriculture's Agricultural Research Service laboratory in Gainesville, Fla.

Fleas are wingless parasites that reproduce in a cycle that frustrates most efforts to get rid of them. They find a host -- perhaps your genial dog -- suck blood and lay eggs. When the dog scratches, the eggs fall off. Just when you think you've killed all the adult fleas on your pets and in your house, their little progeny complete their development and begin looking for a warm-blooded mammal to start the cycle again.

"They develop to a full adult but remain inside the cocoon of the pupal stage" waiting for vibrations or carbon dioxide to alert them to the presence of a host, Patterson said.

It is usually easy to tell when the fleas have arrived. Your dog starts acting like Walt Disney's Thumper Rabbit, your cat loses its sense of elegant repose, and you notice small red bumps on your legs or your children's legs.

If you want confirmation, you can ruffle your pet's fur, looking for the fleas themselves or for "flea dirt," tiny black crescents of excreted, dried blood.

Fleas will climb aboard a human for a blood meal, but they don't reproduce on humans, said Patterson. They infest cats more heavily than dogs but bother them less. "A kitten we had picked up last night produced 6,000 flea eggs," Patterson said. Both cats and dogs appear to attract more fleas as kittens and puppies than as adults. Then, in old age, they begin to attract fleas again and often develop an allergy, too.

There are several approaches to controlling fleas, many of which provoke vigorous arguments between those who swear they work and those who swear they don't. Most promising is a new generation of insecticides that have only recently become widely available: They take longer to kill the adult insects but also act against their offspring, using a flea juvenile hormone. When the hormone is present in larger than normal amounts, it keeps the larvae from developing into adult fleas.

Juvenile hormones are expected to be the "bug killers of the future," according to Chemical Week. It focused on two reasons: "The compounds are generally insect specific, and insects should be hard pressed to develop resistance to them, as they produce the compounds themselves."

Chemical Week mentioned two products on the market that use this Peter Pan approach to eliminating adult fleas. S.C. Johnson's Raid Flea Killer Plus is made of a mixture of pyrethrins, insect-specific nerve toxins that come from chrysanthemums, combined with juvenile hormones. Black Flag's Flea Ender is a mixture of pyrethrin analogue and juvenile hormone analogues, according to the magazine. Still another pesticide that uses the growth inhibitors is Precor, produced by the Zoecon Corp., which also provides the analogues for the Black Flag products.

The juvenile hormone growth inhibitors "work very, very well, especially when it's combined with something like Dursban or some other knockdown agent" to kill adult fleas, he said. "For the first time people are able to give guarantees with flea control."

Patterson said that his surveys have found that fleas in Florida have developed resistance to virtually all chemicals used for their control except for dursban, an organo-phosphate. His research indicates that pyrethrins knock the fleas off of animals but that they revive and jump back on. Growth inhibitors have proven to be the best approach for killing fleas indoors, according to Patterson. But he cautioned that they will not kill fleas in the yard because the products currently on the market break down with exposure to sunlight.

At Friendship Hospital, where the staff spends a lot of time bathing and spraying frantic pets, Goble recommends making sure that a flea-free pet goes back to a flea-free environment. "People sometimes ... bring the animal here to be deflead and forget about the car," she said. "The fleas hop right back on, and the whole cycle starts again."

Friendship sells Siphotrol Plus, a combination of Dursban and Precor, for exterminating fleas in the house. The clinic also recommends Vet Kem flea and tick spray, with a pyrethrin base. Although some people dispute whether chemical flea collars work, Goble maintained they are effective as part of a total flea control program. But they won't eliminate the problem by themselves, she said.

Patterson said his research has shown the ultrasound collars to be worthless. The lab tested 18 different types of products that purport to control fleas, roaches or rodents using ultrasound. "Not one caused the insects to flee from the area," he said. The products might stimulate random movement by the insects, but "none of them work," he said. The Federal Trade Commission has issued complaints against several manufacturers of ultrasound devices designed to control roaches and rodents saying that the products did not live up to their claims.

Jan Wheeler, a senior correspondent with Organic Gardening magazine's research and reader service center, said that they recommend an insecticidal flea soap manufactured by Safer Agro-Chem Ltd. The magazine also recommends diatomaceous earth, an organic powder sold by a number of gardening supply companies. The powder is made of sharp particles of algae skeletons that can be sprinkled on the dog and on the carpet to control fleas, she said.

Many natural treatments for flea control rely on strong fragrances, such as citrus oil. Organic Gardening also suggests steeping half a cup of fresh or dried rosemary in a quart of boiling water for 20 minutes, letting it cool and then pouring it evenly over the dog or cat "if they allow it." Wheeler said to let the fur air-dry rather than toweling it dry, which would remove the herb residue.

"If your pet has dry skin, you can use oil of thyme, eucalyptus or pennyroyal with an equal amount of olive oil," she said. Still another approach is to feed your dogs or cats brewers yeast or garlic. Wheeler said that she feeds her dogs garlic and has never had a flea problem. But she also said pyrethrins and rotenone are relatively environmentally benign approaches to flea control. Pyrethrins should not be used by people who are allergic to ragweed, however, according to some manufacturers instructions.

The herbal and diet supplement approaches get mixed reviews on their effectiveness. Some of Friendship's clients report good results from using sulphur oil as a food supplement, Goble said. "We have not found it to be very successful."

"It's really hard to get a controlled study of flea control because the situations are so different," she said. "There really are dogs and cats who attract fleas and others who don't."