Fly Control in Kennett Square: Phorid Flies and the Other Flies Indoors

Phorid flies come from the farms, not from your house

This page covers fly problems for the four towns on our Kennett Square pest control page, which is part of our West Chester service area and listed on our Chester County page.

The mushroom phorid fly is a tiny dark fly, 1/64 to 1/8 inch long, with a humped back. Penn State Extension notes dark eyes, where a fruit fly's are red. It breeds in mushroom compost with growing mycelium, and the Pennsylvania Department of Agriculture says it can destroy 10 to 40 percent of a mushroom crop. When numbers build in the growing houses, adults escape, and wind can carry them several miles.

Phorid flies cannot breed in your house. Penn State calls the indoor problem an invasion rather than an infestation, and adults live only a few days indoors, so the flies you see came in from outside.

Why they end up inside Kennett-area homes

Phorid flies are drawn to light, both daylight and ultraviolet. They also climb upward on vertical surfaces, which is why upper floors and attics collect them, and they need humidity, so they stay in bathrooms. One Kennett Square resident told the Philadelphia Inquirer the flies were in the exhaust vents, on the light fixtures and under the shampoo bottle in the shower.

Penn State reports populations spike in September and October, when cool, humid weather lets adults live longer outdoors. Freezing weather knocks numbers down over winter.

The quarantine and the township resolutions

On December 18, 2024, Kennett Township declared the phorid fly infestation a public health and economic emergency, and Kennett Square Borough, Avondale, West Grove and New Garden Township followed with their own declarations. On January 30, 2025, the Pennsylvania Department of Agriculture issued a quarantine order for Kennett and New Garden Townships requiring mushroom farms to steam off growing houses, heating them enough to kill flies and larvae.

Kennett Township staff still received numerous complaints in fall 2025, and on February 4, 2026 the township adopted Resolution 2026-8, re-declaring the emergency and asking state and federal agencies for more research and stronger controls at the source. The township's own briefing notes that Pennsylvania law gives local governments no authority over the farms.

What you can do at home

These steps come from Penn State and University of Maryland Extension guidance, applied to Kennett-area houses.

• Repair screen tears and gaps where the screen meets the frame. Keep windows closed during peak weeks if flies get past the screen.
• Check bathroom and kitchen exhaust vents, dryer vents, window air conditioner edges, attic vents and gaps around pipes and wires where they pass through siding. Seal with caulk or fit covers that close.
• Close blinds at night so indoor light doesn't pull flies to the glass.
• Place sticky traps on windows and a light trap indoors in the rooms where flies gather. Vacuum flies off windows and bathroom surfaces.
• Skip the bug spray. Penn State advises homeowners against using chemical insecticides for phorid flies indoors.
• If flies keep appearing near one sink or tub, the drain may be breeding drain flies. Scrub the drain and trap with a stiff brush. Tape a plastic bag over the opening overnight; flies in the bag mean that drain is the source.

What a visit can do, and what it can't

A visit starts with The Davis Inspection Standard: identify the species before anything is applied. That matters here because a fly that looks like a phorid may be a drain fly, fruit fly or fungus gnat breeding inside the house, and those can be fixed at the breeding site. Then we walk the house for entry points, screens, vents and light, set traps where flies collect, and place any treatment only where the label allows at the openings they use. You get re-entry and prep instructions up front and a follow-up date.

Indoor treatment reduces the flies inside your home, but it cannot fix the source on the farms, and new flies will keep arriving while fall numbers are high. The farm source is what the Pennsylvania Department of Agriculture quarantine and the townships are working on.

Cluster flies, drain flies and house flies

Not every fly problem in Kennett Square is a phorid. These are the three other common indoor flies, and each has a different fix.

Getting help with flies in Kennett Square

Catch a few flies on clear tape before you call (610) 935-9130 or use our contact page. Cluster flies overwintering in the attic are part of our stink bug and fall invader control. Restaurants, farm stands and shops dealing with house flies can start with commercial pest control. We are licensed with the Pennsylvania Department of Agriculture and insured.