Fly Control: Get Rid of House Flies, Cluster Flies and Drain Flies

Flies buzzing around the kitchen, collecting on a sunny window in March or hovering over the bathroom sink are three different problems with three different fixes. Trying to swat or spray your way out rarely works because new flies keep coming from wherever they breed. This guide helps you figure out which fly you have, find where it is coming from and get rid of it with the least effort.

How to identify common house flies

Start with where you see the flies and what they look like. Tiny flies hovering around fruit bowls or the trash are usually fruit flies, which have their own fruit fly guide.

House flies have sponging mouthparts and cannot bite. If you are getting bitten by flies outdoors near grass clippings or compost, you may have stable flies, which do bite and breed in moist clippings and compost.

Signs of a fly problem

• More than a few flies indoors on most days.
• Flies gathered around the garbage, the compost pail or the pet’s outdoor area.
• Dozens of slow flies on sunny windows in late winter or early spring (cluster flies).
• Small fuzzy flies resting on bathroom walls or a shower near the drain (drain flies).
• A sudden burst of large shiny flies (blow flies). They develop in carrion, so a dead animal in a wall, attic or crawlspace is worth ruling out.

Why flies show up

Almost every fly you see inside came from outside or from a breeding spot you can find. House flies breed in warm, moist organic matter. In summer, a house fly can go from egg to adult in as little as a week, and each female lays several batches of 100 or more eggs, so a forgotten trash bag or a pile of dog droppings can produce a lot of flies fast.

Cluster flies are a different story. They spend the summer outdoors, then look for sheltered places to spend the winter in late summer and fall. They squeeze into attics and wall voids through small gaps, seem to favor light-colored buildings, and come out when indoor heat or a sunny day warms them up.

Drain flies live their whole lives near the slime that coats the inside of drains, so they usually point to one particular drain.

Risks

House flies land on garbage, feces and rotting matter, then on food and counters, and they can carry germs that cause diarrhea, food poisoning and eye infections. That is a good reason not to tolerate them in the kitchen.

Cluster flies and blow flies found in homes in late winter are not breeding indoors and are not a health hazard. They are a nuisance. Drain flies are also mostly a nuisance, though very large numbers have been linked to allergies.

How to get rid of house flies

Work through these steps in order. Sanitation does most of the work, and traps help with the stragglers.

1. Find the breeding source. Check trash cans (including the bottom), recycling bins, compost, pet waste in the yard, grass clipping piles and any rotting produce.
2. Fix the garbage. Bag household trash, keep outdoor cans tightly lidded and away from doors, and do not let garbage pile up. Rinse cans that get dirty.
3. Clean up organic waste outdoors at least once a week. Pick up dog droppings, and do not leave grass clippings or fallen fruit to rot.
4. Screen and seal. Fit tight screens on windows and doors and seal cracks around frames. Keep doors closed.
5. Use the right trap for the job.
   • Sticky fly ribbons work for a few flies in a small room. They will not handle a heavy problem.
   • Baited cone traps work outdoors when there is no garbage nearby competing with them. They smell strong, so hang them away from the house.
   • Ultraviolet light traps can catch flies indoors when placed away from windows and daylight.
   • A swatter is fine for a few flies, just not over food or prep areas.
6. Spray only if you cannot fix the source. A non-residual pyrethrin aerosol kills flies that are present. Fly baits around trash areas help only when sanitation is also in place. Read and follow the label.

Traps only catch adults. Sprays only kill them. If you skip the garbage and pet waste cleanup, new flies hatch every week and you will be trapping all summer.

Keep bug zappers away from kitchens and food prep areas. They can scatter insect parts.

How to get rid of cluster flies

Cluster flies are hard to eliminate once they are inside the walls. Prevention before fall works best.

1. Seal entry points in late summer. Caulk cracks around windows, baseboards, siding and other small openings, and screen attic soffit vents. Loose siding gives them easy access, and ordinary window screens will not stop them.
2. Vacuum the ones you see. A vacuum is the easiest way to deal with flies on windows. Empty it outside.
3. Open attic windows on sunny days to let flies leave on their own.
4. Consider an outdoor treatment. A residual insecticide applied by mid to late August to the outside surfaces where flies rest can reduce the number that get in. Some sprays can stain siding. Read and follow the label. This is often a job for a professional.

An indoor pyrethrin spray kills only the flies it hits and leaves little residue behind. Most of the flies stay hidden in wall voids.

How to get rid of drain flies

Drain flies point you to a dirty drain, and the fix is cleaning it.

1. Find the drain. Check sinks, tubs, showers, floor drains and the condensate line from the air conditioner. To test a drain, coat the inside of a clear plastic tub with a thin layer of petroleum jelly and set it upside down over the drain overnight. Flies stuck inside the next morning confirm the source.
2. Scrub out the slime. Use a stiff, long-handled pipe brush to scrape the gel-like film from inside the pipe. Removing the trap first, or using a plumber’s snake, can help with hard-to-reach drains.
3. Use a biological drain cleaner to break down what the brush cannot reach. If you have a septic system, check that the product is safe for it. Read and follow the label.
4. Keep it clean. Do not let sludge build up again, and keep garbage pails dry and clean.

Insecticide sprays kill a few adults for a short time and leave the larvae breeding in the drain.

When to call a professional

Most house fly and drain fly problems are DIY jobs. They end when you remove the breeding source. Call a licensed pest control company if:

• Cluster flies come back every year in large numbers. A pro can treat the outside walls in late summer and find entry points you missed.
• You see blow flies suddenly and suspect a dead animal in the walls, attic or crawlspace. Someone needs to find and remove it. If the animal is still alive, our guides to squirrels and raccoons cover removal and sealing.
• You run a restaurant, food business or farm, where the breeding source can be harder to track down.
• Flies keep coming after you have cleaned up, and you cannot find the source. A pro may use light traps to pinpoint where drain flies are most active.

A good visit starts with an inspection for breeding sites and entry points, not a spray. Ask the technician what they found, where the flies are breeding, what they plan to apply and whether you can see the label. Our guide to choosing a pest control company lists the questions to ask, and integrated pest management explains why inspection and sanitation come before any treatment.

Fly questions

Why do I have so many flies in winter? Those are most likely cluster flies coming out of the walls or attic on warm days. They are not breeding in your house. Vacuum them up, and seal the house next summer before they move in.

Will bleach or boiling water get rid of drain flies? Not by themselves. Scrub the slime out of the pipe first; hot water can then flush out what is left. Never pour bleach after a caustic drain cleaner, because the mix can release chlorine gas.