According to some entomologists, bug zappers are not only 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 percent - were biting bugs "seeking blood meals at the expense of homeowners."

Nearly half were non-biting aquatic insects such as caddisflies and midges that feed fish, frogs, birds and bats, the study found. And another 14 percent were insects that actually attack pests, such as wasps, ground beetles and ladybugs.

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, more than 71 billion nontarget insects are needlessly destroyed in the United States each year.

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