Question: Help! As spring approaches I dread the thought that nasty house flies will again invade my house. A few flies, I expect, but I think that chasing after and killing up to 20 flies a day inside is a problem and one that I hope you can give me some advice on. They’ve returned to my house for three springs/summers now. What can I do to stop their return? Thanks!
ANSWER: Most likely you have seen cluster flies. Often mistaken for house flies, they have a completely different life cycle. Cluster flies are very common inside homes in the spring time.
The life cycle of the cluster fly (Polenia rudis) begins in the spring when they leave the overwintering sites (attics and wall voids of houses) and lay their eggs in the soil. The larval or maggot stages of this fly attack and eat earthworms. There are several generations of cluster flies during the summer, and each time the female returns to lay eggs in the soil.
However, the flies of the last generation (mid to late August) will spend the winter in a protected location, and start the life cycle over again in the following spring. They begin searching for a place to spend the winter during the last month of summer. They will seek out the sides of houses that are warmed by the afternoon sun, and collect there by the hundreds or thousands. They spend the winter inactive in attics and wall voids. They become active again when temperatures become warm.
In the spring, inspect the outside of the house. Seal up any openings that the flies might use to get inside. Make sure screens and weather stripping are in good condition. Make sure that attic and crawl space vents also have screens.
For assistance and treatments call your local Orkin Branch Office.