Do ultrasonic bug repellers work?

Dear Cecil: A friend of mine has been having some trouble lately with that perpetual pest, the mosquito. He remembers reading somewhere — as do I — about some kind of ultrasonic transmitter used as a mosquito repellent. Do these devices work? Do they have any effect on humans? Are they legal? And where can I get one? I’m just itching for your reply. Hot to Swat, Chicago

Cecil replies:

I’m not going to answer your last question, H., because ultrasonic mosquito repellers all have one thing in common: none of them work. At all.

Ultrasonic devices work, according to one advertisement, by “mimicking the sound of the bat — the mosquito’s greatest enemy.” (They emit sound in the 20-50 kiloHertz range, higher than humans can detect.) While it’s true that bats eat mosquitoes and that bats make ultrasonic sounds (they navigate through a sort of natural radar), the humble mosquito apparently can’t make the connection. The U.S. Environmental Protection Agency conducted two years of tests in the mosquito-ridden area around Chesapeake Bay, trying virtually every type of electronic repeller they could lay their hands on. Not a one had any noticeable effect on mosquitoes, or, if it’s any comfort, on humans (although some say the latter question hasn’t been studied in sufficient depth). Subsequent research at various universities has pretty much borne out the EPA’s findings. Both the EPA and the U.S. Postal Service have gone after ultrasonic repeller makers for making unsupported claims for their products.

Some ultrasound firms say their products will also repel mice, rats, roaches, bats, fleas, spiders, and the like. The evidence to date suggests these claims are greatly exaggerated. At best they work only when used in conjunction with a concerted anti-pest program involving traps, improved sanitation, elimination of entry points and nesting places, and so on. So don’t throw away that flyswatter yet.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.