The best bug zappers for flies

Why zappers work on flies and fail on mosquitoes

A bug zapper is an ultraviolet lamp with an electrified grid around it. Everything about its performance follows from one question: does the insect you want dead navigate toward UV light?

Flies and moths do. They are strongly phototactic, they fly in daylight and at dusk, and they will cross a yard to a bright lamp. A grid zapper kills them in quantity, and you can hear it doing so.

Mosquitoes largely do not. Host-seeking females navigate by carbon dioxide, body heat, moisture and skin odor — you, in other words, not a lamp. The classic University of Florida extension write-up on the subject put it bluntly in its title: electric bug zappers are useless for controlling mosquitoes. Repeated counts of what zappers actually catch find the overwhelming majority is harmless non-biting insects, with mosquitoes a tiny fraction of the total.

So the honest framing is this: a zapper is a fly and moth machine. Bought for flies, it does the job. Bought for mosquitoes, it will disappoint you and kill a great many beneficial insects on the way. We set the whole argument out in do bug zappers work, and if mosquitoes are your actual problem, start at best mosquito traps or best yard mosquito repellents instead.

What to look for

Lamp area and coverage, matched to the space. Coverage figures are manufacturer claims measured in open air, so treat them as a size class rather than a measurement. Here is how our picks compare on the makers' own numbers:

Indoor or outdoor — they are not interchangeable. Outdoor units are weather-sealed and bright enough to compete with dusk. Indoor units run on tubes sized for a room and have a tray to catch debris. An outdoor zapper indoors is far too bright to live with; an indoor unit outdoors fails in the first rain.

A debris tray you can remove. This is the difference between a zapper you keep using and one you unplug in August. Grid zappers produce a tray of insect debris that has to be emptied.

Hanging height and position. Most makers specify a height, typically head height or a little above, and a position away from where people sit. Both matter more than the wattage.

Replaceable bulbs. UV output falls off long before the lamp stops lighting. Budget a bulb roughly annually on a unit that runs all season, and check the bulb is actually available for the model.

Noise and debris tolerance. A grid zapper snaps. In a garage or a barn that is irrelevant; three feet from a dinner table it is not. The silent alternative is a UV light over a glue card, which catches the same flies with no noise and no scatter — for an indoor room, that is often the better buy.

Where to hang a zapper so it works

Placement decides most of the result, and the common instinct — hang it right where the people are — is wrong.

Outdoors:

• Away from where you sit, not above the table. You want flies drawn to the zapper rather than through your seating area.
• 30 to 40 feet from the patio is a reasonable compromise, with the unit between the seating and whatever is producing flies: the cans, the compost, a dog run, a coop.
• Head height or just above, hung from a branch, post or bracket with clear air around it.
• Away from floodlights and porch lights, which drown the UV out and give insects a brighter target.
• Run it continuously through the season. Switching it on for an hour catches a fraction of what a continuous run does.

Indoors:

• Near the source, which in practice means the trash cans, the drain or the door flies come in through.
• Away from the main sitting area, and away from dust: a glue card or a grid loads up with sawdust just as happily as with flies.
• Not facing a bright window. Any UV trap competes with daylight and loses.

Set expectations honestly

A zapper will not clear a space of flies on its own, because it kills adults and does not touch the breeding site. Flies breed in moist decaying organic matter, and the egg-to-adult cycle can run in about a week in warm weather. So pair the machine with the two fixes that matter:

1. Lids on every trash and recycling can, and rinse them. Dried residue in the bottom of a can is a breeding site whatever the lid does.
2. Clear the damp organic matter — floor drains, compost caddies, grass clippings in bags, drips under a freezer, pet waste in a yard.

The best fly traps for a garage covers that geometry in detail, and how to get rid of house flies is the full indoor method.

Also know what a zapper cannot help with. Fruit flies in a kitchen come to fermentation, not light, so a liquid lure trap beside the fruit bowl beats a zapper every time — see best fruit fly traps. Fungus gnats off houseplants need a fan trap and a soil treatment, covered in best gnat traps. And drain flies need the drain cleaned.

The ecological cost, stated plainly

We think this belongs on the page rather than in a footnote. A large outdoor grid zapper running all season kills thousands of insects, and only a small proportion of them are anything you wanted dead. Moths, beetles, lacewings, parasitic wasps and midges that feed birds and bats make up the bulk of the catch.

If that matters to you — and it should at least be a consideration — there are two ways to reduce it without giving up fly control:

• Use an indoor unit indoors, where the catch is limited to the insects that have already come inside, rather than a yard-scale zapper that draws insects in from the whole neighborhood.
• Use a sticky UV light instead of a grid, which catches the flies in the room and nothing from outside.

Both are better buys for most houses than the biggest unit on the shelf. The acre-rated zapper earns its place around a barn, a coop, a kennel or a yard with a genuine daytime fly problem — not on a suburban patio where the real complaint is mosquitoes.