This summer because of the threat of West Nile virus, the city is undertaking the first large-scale spraying for adult mosquitoes since 2002 -- only the second since 1975 -- and residents' response to the spray trucks has ranged from protests and screams to friendly waves and thumbs-up signs.

The chemical, often known as Sumithrin or by the trade name Anvil, is similar to commercially available bug bombs and products that kill head lice.

Although they are all cooked-up versions of the natural insecticide produced by chrysanthemums, there is little debate that exposure to large amounts is unhealthy. Symptoms range from a rash or cough to respiratory distress and death.

'No Black Helicopters'

It's the miniscule amount sprayed by cities that leads to heated arguments, at least in Chicago.

"In the suburbs, people go to the city council and protest why we're not spraying in their area," said George Balis of Clarke Mosquito Control, the Roselle company that sprays for Chicago and 200 surrounding communities.

"In the city, there's the feeling that there must be something behind it," he added, sounding exasperated at the conspiracy theories that surround his work. "There are no black helicopters."

A lone truck sprayed Tuesday night in Bloomingdale Township and appeared a bit clock-and-dagger as it rolled slowly down a dark street spraying a chemical mixture out of a rear-mounted tank. The spray's fog glowed in the truck's flashing yellow lights before dissipating.

Clarke, the largest mosquito control company in the United States, does not disclose the inert ingredients that it uses in its chemical cocktail. But Anvil, the sole active ingredient, makes up about 10 percent of the mixture.

Clarke uses Anvil in minute amounts: 0.62 ounces per acre. But even small amounts can kill fish and bees, and Anvil has been shown to have varying effects on humans, said Caroline Cox, staff scientist with the Northwest Coalition for Alternatives to Pesticide.

Compare these statements with those of Balis, who recently said that drinking a spoonful of Anvil would leave you with nothing more than a bellyache, and the controversy begins to form.

All Kinds of Reactions

Officials with the US Environmental Protection Agency come down somewhere in the middle, saying Anvil and similar products "pose minimal risks to human health and the environment when used according to label directions."

They do, however, recommend staying indoors, closing windows and turning off air conditioners while spraying is going on.

At Hanover Park, where spraying has taken place, three out of four people who were questioned said they supported spraying.

"One of my sister's friends got West Nile, so I'm glad they spray," said Kristin Drogos, 24, of Roselle.

"We've got a mad reduction program in Oak Park," Andrea Harder, 24, said.

Tim Hadac, the Chicago Department of Public Health spokesman who fields much of the criticism and praise on the issue, said spraying creates all kinds of reactions.

"For every anti-spraying call we get, we get a call saying people want the spraying," he said. "I think that's our challenge -- to keep explaining what we're doing and why we're doing it."