Where Do Flies Go in the Winter?
Most flies live their lives in spring and summer, and then die. In cold climates, only a few adult flies hibernating in sheltered places survive the winter. Warm weather awakens them and they seek places such as garbage cans in which to lay their eggs. A female fly may lay up to 150 eggs at once.
The eggs hatch into worm-like larvae, called maggots. After feeding on garbage, the maggots become pupas. Within six days, a pupa becomes a full-grown fly, each female ready to produce eggs. And very soon, those eggs are full-grown flies, too.
Many of these flies are muscids, which include the blowflies or bluebottles, and their relatives such as the common house fly (Musca domestica). Most spend the winter as adults in cracks and crannies and wake up in spring to lay their eggs on decaying matter.
House flies delight in unhygienic places, and their maggots feed on rotting food and other human waste.
Cluster flies often enter houses in large number and spend the winter in large huddles in the corner of a spare room or loft. Like all insects they don’t truly hibernate, but enter a state of diapause, which slows down their development and appetite, until temperatures rise and they become active again.
Unlike their relatives, cluster flies don’t lay their eggs on rotten flesh or excrement, but instead have a surprising taste: earthworms. In autumn, the flies lay their eggs in the soil and, on hatching, the maggots search for a host. Once inside the earthworm, they eat their way from one end to the other and back again, and pupate in the shell of their hollowed-out victim.