Sudden house fly explosion — what usually causes this?

Hi all,

hoping to get some insight here. Over the past few days, my house went from seeing an occasional fly to suddenly having a ton of them, especially near windows and the kitchen. Nothing obvious has changed — trash goes out regularly, no pets, and the place is generally clean.

I’m trying to figure out what typically causes a sudden spike like this and whether it’s something inside the house or more likely coming from outdoors. Any ideas on where to start looking?

This usually points to something attracting them nearby, not necessarily poor hygiene.

I had this happen once and it turned out something had died in a crawl space.

Weather changes can trigger it. Warm spells after rain seem to make flies pop up fast.

Outdoor bins, compost, or even a neighbor’s setup can cause indoor problems.

They tend to gather near windows because of light, even if they didn’t come in there.

Check floor drains and unused sinks. Those get overlooked a lot.

@OldBasementGuy Same here. The source wasn’t obvious at all until we checked hidden areas.

@SeasonShift We did have heavy rain last week followed by heat.

Small gaps around doors or vents can let a surprising number in.

@HomeMaintenance101 good call. Drain issues are a common but invisible trigger.