How to get rid of mosquitoes in the house

First, work out which problem you have

The two causes need completely different responses, and the count tells you which you are dealing with.

One or two a night, worse when the doors have been open: they are coming in from outside. This is by far the more common case, and the fix is at the openings and in the yard.

Several every evening, or they keep appearing in a room with the windows shut: something indoors may be producing them. This is the less common case — most houses have no indoor breeding site at all — but it is the one that explains a problem that will not stop. Mosquitoes can complete the cycle from egg to adult in about a week in warm standing water, and a house has more standing water in it than people realise.

They appear in a basement, a bathroom or a utility room specifically: suspect an indoor breeding site immediately. A sump pit, a floor drain, a laundry tub trap or a rarely used shower drain all hold water, and species that breed in dark containers will use them happily.

One more check worth doing: if they are tiny, fuzzy and sitting still on the bathroom wall rather than flying at you, they are drain flies, not mosquitoes — drain flies in the sink is the page you want. If they drift up off a houseplant, they are fungus gnats: best gnat traps.

Clearing the room tonight

Mosquitoes indoors are not hard to find once you know where they rest. They spend most of the day on vertical surfaces in dim, still, humid places:

• Behind and under furniture, especially the bed and the sofa
• Behind curtains and blinds
• In the lower corners of walls and behind doors
• In closets, under the stairs and in the bathroom
• Around laundry hampers and anywhere a little damp

What works, in order:

1. An electrified racket. For the one that woke you up, this is genuinely the right tool: aimed, instant and no chemicals in a bedroom. Switch a light on behind you and watch the wall rather than the air. Best electric fly swatters ranks them.
2. A UV fan trap, overnight, with the room lights off. Indoor traps only compete with darkness, so they earn their keep after bedtime. Place it at floor to waist height in the room with the problem, away from the window, and leave it running. Best indoor mosquito traps covers the category.
3. A fan. Underrated and free. Mosquitoes are weak fliers and will not hold a course in moving air, so a ceiling fan or a box fan at the bed makes a room much less bite-prone while you deal with the cause.
4. A plug-in sticky light if you want something passive running in a hallway or kitchen continuously.

What not to do indoors: aerosol space sprays give you an hour and nothing else, and outdoor-scale electric zappers are both too bright for a room and the wrong tool for mosquitoes anyway — see do bug zappers work.

If they are getting in: close the routes

Go around the house once, ideally at dusk with a flashlight, and look at every opening at mosquito scale. A gap you can see daylight through is a gap.

• Window screens. Check for tears, gaps at the frame edge, and screens that no longer sit flush. Standard insect mesh is fine; nothing finer is needed for mosquitoes.
• Door sweeps and thresholds. The gap under an exterior door is the commonest single route.
• The screen door latch. A screen door that does not close itself is a door that stands open.
• Bathroom and kitchen extract vents, and the dryer vent — fit a screened cover, and never block the duct itself.
• Attic and crawl-space vents with damaged mesh.
• Window air conditioners, where the side panels and the gap around the unit are usually the problem.
• Unscreened basement hopper windows, and the gap around a basement door.
• Gaps where pipes and cables enter at ground level.

Then reduce the pressure outside, because every mosquito that is not in your yard is not at your door. Standing water is the whole story: some species breed in a container the size of a bottle cap in about a week, so walk the property weekly and tip out plant saucers, buckets, toys, tarps with a sag, bird baths and the gutters. Treat water you cannot drain — a rain barrel, a pond with no fish, a wet low spot — with BTI, a bacterial larvicide specific to mosquito and fly larvae that the EPA approves and that is harmless to fish, pets and birds. What attracts mosquitoes lists the sites people miss, and how to get rid of mosquitoes in your yard is the full outdoor campaign.

If something indoors is breeding them: find the water

This is the case people chase for weeks because they keep killing adults. Go looking for water that has been sitting for more than a week.

• Plant pot saucers and cachepots. The most common indoor breeding site by a wide margin. Empty them; do not just tip the excess back into the pot.
• The tray under a self-watering planter, and hydroponic or propagation jars.
• A basement sump pit. Standing water with a lid that does not seal is ideal habitat. BTI granules are the right treatment here.
• Floor drains in a basement, garage or laundry room, especially ones that are rarely used.
• Rarely used sink, tub and shower traps in a guest bathroom.
• The condensate tray under a fridge, freezer, dehumidifier or air handler.
• A washing machine drain pan, and the bottom of a laundry tub.
• Water left in a bucket, mop bucket, pet bowl, vase or watering can indoors.
• A crawl space with standing water under the house. This counts as indoors for these purposes and is worth a look with a flashlight.

Empty what you can, treat what you cannot. BTI granules are the appropriate product for a sump, a floor drain or damp soil — they act on the larvae rather than the adults, so they stop production rather than cleaning up after it. For houseplant soil the same granules do double duty, because BTI also kills fungus gnat larvae.

Protecting a bedroom

If you are being bitten at night while you sort the cause out:

• Run a fan at the bed. Moving air is the simplest barrier there is.
• Close the bedroom window at dusk specifically — that is the hour most species are moving.
• Repellent on exposed skin if you are getting bitten, per the CDC's bite-prevention guidance. A 20% picaridin product is pleasant enough to use on skin indoors, and kid-safe mosquito repellents covers the age limits.
• A bed net is worth considering for a child's room during a bad spell, and it is the only approach that needs nothing switched on.
• Do not burn coils indoors. They are an outdoor product, and the smoke is not something to sleep in.

What to expect

Getting the adults out of a room takes one evening with a racket and a trap running overnight. Stopping the supply takes the screens and door sweeps, which is an afternoon. If the cause is an indoor breeding site, expect a lag: adults already flying will keep appearing for several days after you have emptied or treated the water.

If you are still finding several a night a fortnight after doing all of this, the water is somewhere you have not looked. The sump, the crawl space and the condensate tray are the three that hide the longest.