Bug Zappers Work Only Too Well, According to Study


Spring has arrived and daylight savings time is here, so can the mosquitoes be far behind? For many Americans, it’s time to get out the electric bug zapper.

The continuous snap, crackle and pop coming from a zapper on a summer evening has persuaded many homeowners that the traps are effective in ridding porches and patios of marauding mosquitoes and no-see-ums.

But wait, say some scientists who study insects. Too often, they believe, bug zappers not only are ineffective against biting bugs, but do more harm than good.

For instance, a study by the University of Delaware at Newark analyzed 13,789 insects zapped by electric traps and found only 31--less than one-fourth of 1%--were biting bugs “seeking blood meals at the expense of homeowners.”


Nearly half were non-biting aquatic insects such as caddis flies and midges that feed fish, frogs, birds and bats, the study found. Another 14% were insects that actually attack pests, such as wasps, ground beetles and ladybugs.

“The heavy toll on nontarget insects and the near absence of biting flies in catches suggest that electric insect traps are worthless for biting-fly reduction,” said Douglas W. Tallamy and Timothy B. Frick, who conducted the study.

Tallamy, an entomologist, said insects have been described as the glue of the ecosystem.

“They are such an important component of the food chain that, if removed, the ecosystem would fall apart,” he said. “If you remove the source of food for birds and fish, you don’t have birds and fish anymore. A number of mammals also depend on insects.”

Sal DeYoreo, president of Flowtron Outdoor Products, a manufacturer of electric traps in Melrose, Mass., disputed the Delaware study.

“The findings and numbers in the study are inconsistent with those of the owners of the bug killers,” he said.

DeYoreo also contended that zappers “are a safe alternative to chemical insecticides, which when sprayed, kill all in their path,” including breeding sites. And insecticides have the added danger of affecting the bird food chain by poisoning insects, he said.

The Delaware study estimated that about 1 million zappers are sold in the United States each year. The traps used in the project had been operating for an average of seven years.

Through the 40 nights of the study, the seasonal mean catch per night was 445 insects per trap.

That means that if, in any given year, 4 million traps are used for 40 nights during the summer, then more than 71 billion nontarget insects are needlessly destroyed in the United States each year, the study concluded.

Some entomologists say the study suggested that since so many predators and parasites were killed, the traps may actually be protecting mosquitoes and other pests.

Electric traps typically use ultraviolet light to lure flying insects to an electrified metal grid, which Tallamy said does not attract mosquitoes and explains why so few were found in the traps.

But he said one of the most important reasons for the traps’ failure is that mosquitoes are far more attracted to the carbon dioxide exhaled by people.

DeYoreo said newer, state-of-the-art traps use lures similar to cows’ breath that are more attractive to biting bugs.

But if you have a problem in killing insects, what’s the alternative?

“I personally have no trouble using standard insect sprays,” said Tallamy, the entomologist. “Another thing is modifying your behavior, staying away from where mosquitoes are. Citronella works somewhat. Campfire smoke does too.”

Tallamy and Frick, then a university student, conducted the study during the summer of 1994 in lowland, wooded areas near aquatic breeding habitats in suburban Newark, Del. Their findings were published in Entomological News by the American Entomological Society in Philadelphia.