I like to think that I’m a reasonably open-minded person—neither credulous nor rigidly skeptical. When a friend of mine told me he saw ghosts, I didn’t try to convince him he was hallucinating; I believe that he had some sort of genuine experience for which the terminology and imagery of “ghosts” provided an appropriate description. I would be reluctant to say that what he saw were really spirits of the departed, but then, things are frequently not what they seem; lacking solid evidence one way or another, there’s no point in being dogmatic.
There are some things, though, that lots of people persist in believing in the face of serious counterevidence. I am speaking, of course, of the decades-old meme that you can keep mosquitos away by using a little electronic gadget that emits ultrasonic sound. Let me get straight to the point: they don’t work. They have been scientifically proven not to work again and again over a period of quite a few years. Yet somehow manufacturers keep making them and people keep buying them, because the claim that they should work seems so plausible (and because they get an astonishing number of fake 5-star reviews on Amazon). As a public service, then, I’d like to tell you the truth about ultrasonic mosquito repellers.
I have always been popular with the girls—female mosquitoes, that is. I don’t know if it’s my charming demeanor or the irresistible smell of Earl Grey tea on my breath, but somehow, if there is a single mosquito buzzing around a crowd of a hundred people, it always manages to find me. My skin is quite sensitive to mosquito bites, too; they turn into big, ugly, insanely itchy welts that don’t go away for days. Fortunately, I live in an area where there are relatively few mosquitoes, but when I’m in, say, Costa Rica in the winter or Saskatchewan in the summer, mosquito avoidance is always a top priority. If I’m staying put, tactics like mosquito netting, citronella candles, and mosquito coils work well, but when I’m moving around there’s no good choice but to cover myself with some sort of mosquito repellent. DEET-based repellents, while effective, are greasy, smell horrible, and supposedly find their way into your bloodstream quite quickly, where they can’t be especially healthy. Newer, more natural alternatives are safer and less offensive to the senses, but it’s still no fun to smear the stuff all over my exposed skin (and keep reapplying every hour or so).
So one summer, I bought myself an ultrasonic mosquito repeller. The package claimed this tiny, battery-powered device was “safe and effective,” and I figured it was worth finding out if I could get relief without all the chemicals. When I took the device out of its package, the first thing I noticed was that it had not only an on-off switch but also a frequency dial. I thought that was odd; wasn’t it supposed to be some precise frequency that drove mosquitoes away? But perhaps I was just thinking about the device in a technologically unsophisticated way.
I took the repeller outside and went to an area that I knew to be popular with mosquitoes. I flipped the switch, and within a few seconds a mosquito approached me, hovering about a foot away. I slowly turned the dial from one frequency extreme to the other; the mosquito was unfazed. I thought it was perhaps a question of range, so I held the device as close as I could to the mosquito. Even an inch away, it had no effect. Finally the mosquito landed on the little black box in my hand and I decided the experiment had been definitively concluded.
The U.S. Environmental Protection Agency and numerous universities have performed tests to determine if or how well various ultrasonic repellers work. In most cases, the tests showed no difference between using the device and using no protection; in the least successful experiments, use of ultrasonic devices increased the number of bites. And the U.S. Federal Trade Commission has clamped down on manufacturers making unsupported claims about these products. So what makes people think they should work, and why don’t they?
Some animals are sensitive to sounds pitched higher than the range of human hearing; ultrasonic whistles are used when training dogs and circus animals, for example, and bats use echolocation to navigate and hunt. The theory behind ultrasonic mosquito repellers is that there is some frequency, or range of frequencies, that mosquitoes can hear—and find distasteful enough to stay away from. For example, some manufacturers claim their devices mimic the sound made by a male mosquito’s wings, the theory being that females who have already mated would try to stay away from them (though it turns out they do not). Others say their devices emit sounds at the same frequency as the wing beats of dragonflies or bats, the mosquitoes’ natural enemies. Unfortunately, the sounds made by dragonflies and bats have no effect on mosquito behavior in the real world. They don’t prevent mosquitoes from becoming lunch for their predators, and they don’t protect you from becoming dinner for the mosquitoes.
Ultrasonic mosquito repellers do one thing remarkably well, however: survive. They have maintained their uncanny ability to transfer money from the pockets of consumers into manufacturers’ bank accounts in the face of terrible odds. Alas, this is a meme that deserves to die. Save your money and rent a copy of The Sixth Sense or The Mosquito Coast.
Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on July 27, 2003, and again in a slightly revised form on September 5, 2004.