A fly problem is almost always a sanitation or moisture problem in disguise. The species matters because each one is telling you about a different source — and spraying adults without finding the source means they're back in 48 hours.
House flies
Larger, slow, and drawn to garbage, pet waste, and uncovered compost. Outdoor sources almost always: dumpster pads, garbage cans without lids, dog yards that haven't been picked up in days. Treatment is fly bait stations, residual on resting surfaces, and — most importantly — fixing the breeding source.
Fruit flies
Tiny, hovering around bananas and the recycling bin. They breed in any fermenting organic matter: a forgotten potato in the back of the pantry, the slime layer in a bottle return bin, the pulp catch in a juicer. We use vinegar traps to confirm activity and find the source — but the cure is removing the food source, not killing the adults.
Drain flies and phorid flies
Tiny moth-shaped flies sitting on bathroom walls = drain flies, breeding in the biofilm in a slow drain. Tiny hunched-back runners that won't fly straight = phorid flies, often breeding in a broken sewer line, a wet wall void, or organic matter under a slab. Phorid flies in a commercial kitchen are an emergency — they signal a structural moisture problem. We use foaming drain treatments and locate the actual source with a UV trace if needed.
If a pest control company quotes you a fly job without inspecting your drains, garbage areas, and moisture sources, find a different company. Real fly control is detective work first, treatment second.