The best plug-in fly traps

How they work, and why light instead of lure

A liquid lure exploits the specific attraction fruit flies have to fermentation. That works brilliantly for fruit flies and hardly at all for anything else.

A plug-in light trap exploits phototaxis — the pull most flying insects feel toward particular wavelengths, around the blue and near-ultraviolet part of the spectrum. Insects approach the light, land on or blunder into a sticky cartridge behind it, and stay there.

The practical difference: a light trap is non-selective in a useful way. It catches fungus gnats, small house flies, midges and moths as well as fruit flies, where a vinegar lure catches almost exclusively fruit flies.

The trade-off is that it competes with every other light source in the room, including the window.

Where a plug-in earns its place

• A kitchen corner away from the window, running continuously so you stop thinking about it.
• A pantry or utility room, which is dim, has an outlet, and is where the bin lives.
• A room with houseplants, particularly the fan-assisted models, because fungus gnats are weak fliers that get pulled in rather than having to land.
• Anywhere a zapper would be intolerable. No snap, no smell, no visible insect debris — the cartridge hides the catch.

Where it does not

• Bright rooms and sunny worktops. Daylight wins, comfortably.
• As the answer to a source problem. It is still an adult-catcher. The drain, the bin and the plant pot are unaffected.
• Outdoors. Wrong scale entirely, and these are indoor-rated units.
• For a single mosquito in a bedroom at 2am. That is an electric swatter job.

The running cost, stated plainly

This is the thing to work out before you buy, because it is the difference between these and every other trap on the site.

The unit is inexpensive. The refill cartridges are a recurring purchase — roughly monthly under continuous use, more often during a genuine bloom. Over a year, the cartridges normally cost more than the trap did.

That is not a reason to avoid them. It is a reason to check the price and availability of the specific cartridge before you commit to a system, because the cartridges are proprietary and the cheap unit with expensive refills is a familiar pattern.

We cannot show prices on this site yet — there is no live price feed connected, and we do not publish numbers we cannot verify, which is explained on how we pick. Check both the unit and a pack of refills at the retailer before you decide.

Light trap versus the alternatives

Getting the most out of one

• Low down, not high. Most flying insects that matter indoors travel low. Waist height or below, and away from a competing light.
• Leave it on. These are designed for continuous running; switching it on when you see a fly defeats the point.
• Give it a week before judging. A light trap builds a catch gradually rather than filling in an evening.
• Replace the cartridge on schedule, not when it looks full. A saturated surface stops being sticky before it looks covered.
• Turn other lights off in that room where you can. You are competing with them directly.

Still the other half of the job

A light trap running quietly in a corner is a comfortable way to manage a fly problem, and it will not end one on its own. The drain, the bin, the plant pot or whatever else is producing the flies still needs dealing with — how to get rid of fruit flies and how to get rid of gnats cover the source work for each.