Flies are a fact of life in Ontario—but they don’t have to take over your home or business. If you think you may be dealing with them, the first step is understanding the issue. The next step is knowing when it’s time for professional help.
Fly & Cluster Fly Control – What You Should Know
Why they appear, what attracts them, and when to take action.
Seeing flies indoors is frustrating, yet prevention is possible.
Where Flies Come From
Seasonal behavior
In Ontario, cluster flies gather on sun-warmed walls in late summer/fall and overwinter in attics and wall voids, then reappear on warm days in fall and early spring.
Entry points
Flies slip through torn screens, gaps at soffits and fascia, attic vents, window/door frames, and utility penetrations—especially on the south/southwest sides of homes.
Shared environments
Garbage/compost areas, recyclables, floor drains, and neighboring properties (farms, food businesses) can increase fly pressure and introduce new activity.
What You Can Do at Home
- Keep windows/doors screened; repair tears and add door sweeps where needed.
- Seal gaps at soffits, rooflines, attic vents, window casings, and utility lines.
- Bag and remove garbage regularly; rinse recycling, especially sweet/greasy containers.
- Store ripe fruit in the fridge; clean spills and food residues daily (including pet bowls).
- Scrub and flush kitchen/bath/laundry drains; remove organic slime where drain flies breed.
- Vacuum slow, sleepy cluster flies you find indoors; empty the vacuum canister outside.
- Reduce exterior night lighting or switch to “bug” bulbs to cut down on attracted insects.
What Attracts Them to Homes
- Fermenting/organic matter: Ripe fruit, food residues, compost, garbage, and recycling films.
- Moisture & drains: Organic buildup (“biofilm”) inside drains, traps, and sump pits supports drain/“moth” flies.
- Warm shelter (cluster flies): Sun-exposed siding, attics, and wall voids for overwintering.
Why Flies Are a Concern
Hygiene issues
House flies can transfer bacteria as they move between waste and food/contact surfaces; fruit and drain flies contaminate food prep areas.
Property risks
Heavy activity can stain walls/windows, foul light fixtures, and lead to maggots in garbage areas if sanitation is missed.
Rapid breeding
Small fly species cycle quickly; missing breeding sites (drains, mops, compost) allows reinfestation even after surface sprays.
Frequently Asked Questions
What exactly are cluster flies, and why do they show up in fall/spring?
They’re larger, slower flies that breed outdoors in soil; adults slip into structures in late summer/fall to overwinter, then emerge on warm, sunny days.
Are the tiny “fruit flies” coming from my sink?
Sometimes. Fruit flies breed on fermenting produce and residues; drain flies breed in the organic slime lining drains. We identify which and target the source.
How do I eliminate drain flies?
Physically remove the slime: scrub inside the drain/throat, overflow, and P-trap; flush with hot water. Enzyme cleaners help after mechanical cleaning.
Do sprays alone fix a fly problem?
No. Sprays only knock down adults you see. Long-term success comes from sealing entry points and removing breeding sources (garbage, fruit, drains), paired with targeted treatments.