Those_Pesky_Flies

Jeff Green | Mar 03, 2005

Feature article March 3, 2005

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It must be getting close to spring - yesterday I had a fly on the inside of the kitchen window. It was a Cluster Fly, who apparently had aroused from winter slumber when the warmth of the sunshine had raised the temperature of its hiding place.

Cluster Flies are about the same size or slightly larger than the ubiquitous House Fly, but while their buzzing and numbers are an annoyance, they do not bite, nor do they breed in the house; to them it is just a safe place for the winter. When the warm days of spring arrive, they emerge, and if on the inside, soon make their presence known by flying blunderingly around lamps, or doing zombie-like bouncing between walls and ceiling, and may drop onto the floor on their backs spinning with irritating buzzing noises. Those that have survived in the spring have made a wrong turn to the inside of the house and have no wish to remain there, but would happily head outside if the temperature is warm enough.

Last fall as the weather moved into autumn, the Cluster flies started to congregate and seek shelter looking for any small crack or crevice that would offer protection. Many seek the small cracks around the windows, and if a window is opened in winter, you may have a number of the inert bodies fall into the room, where the warmth may arouse them. They prefer the south and west sides of a building, and if it is a multi-storey building, it will be the upper stories or the attic where most gather. It is said they emit a chemical that encourages them to hibernate together or cluster, and which will lead subsequent generations to the same location.

Spring and they will leave their hibernation sites and after outdoor mating, the adult female flies will lay eggs in cracks and crevices in the soil. The larvae that hatch from these eggs will parasitize a small, red earthworm (not the large earthworms commonly seen in the soil). The larval stage lasts between 13 to 22 days, after which they enter a pupal stage, which will last about 11 to 14 days - so the life cycle is complete in 27 to 39 days. There may be four generations over a summer. These flies will proliferate in a warm, wet summer especially around well-kept lawns or rich pasture lands where earthworms are abundant.

Adult flies feed on flowers, and they are transient (winter) visitors in houses. They do not bring health-related problems or feed or damage household objects. However, if crushed, they may leave a greasy spot on upholstery, carpet or wood, and gives off the sickly-sweet odour. I dont have that problem as my cat likes to eat any fly it can reach. If it cant reach it, he lets me know that there is a fly that he would like me to knock down! (He also eats spiders, but will not touch the alien Southern Ladybird Beetle).

Observations: What have you seen? Call Jean at 268-2518 or email This email address is being protected from spambots. You need JavaScript enabled to view it..