What could cause an infestation of house flies?

House fly eggs are laid in moist or rotting organic matter such as household rubbish, compost or manure. Once hatched, flies can reach maturity in a very short period of time depending on temperature. read more

From the description, these could be cluster fly as others have suggested, but it could also be a bluebottle fly or a house fly. Without a picture, the description of "small and large" is all relative. read more

The flies are looking for a cool spot to hang out and lay their eggs. I always find the larvaes in my kitchen at spots such as the garbage can and underneath my table. Despite screens on my doors and windows and cleaning my kitchen, it only take one fly to give birth to a swarm of flies. read more