Cluster flies invade homes | Blogs


If a house or other building looks like it has been overrun with hundreds of flies this fall, it’s probably cluster flies. Although they are a nuisance, they cause no harm or harm to people or pets and do not breed indoors.

To help identify them, cluster flies are slightly larger than a house fly, about three-sixteenths of an inch long, and have golden yellow hairs on their bodies. If crushed, they smell like buckwheat honey.

As temperatures drop in the fall, these flies congregate on the south and west sides of buildings during the day to warm up. Many find their way indoors to overwinter, especially in attics or attics.

They may appear to disappear and then reappear on warm winter days when they become active and enter living quarters. This is why the owners assume that they reproduce in the house, but this is not the case.

A frequently asked question is where do cluster flies come from and the answer is soil as they feed on earthworms. Adult females lay their eggs near earthworm burrow openings. After hatching, the larvae move into burrows and enter earthworms to feed. They pupate in the soil and adult flies emerge.

In the fall, adult flies seek out protected areas like tree cavities and buildings to overwinter. They invade attics and penetrate under siding or around windows or other building crevices. Many eventually congregate between walls and can enter rooms through openings in window frames and electrical appliances.

The best way to manage cluster flies is to keep them out of buildings. Where possible, seal cracks and crevices with silicone caulk or silicone latex and use weatherstripping around doors. Areas to focus on are around windows, doors, siding, utility pipes, behind chimneys and under fascia. Repair damaged screens.

Indoors, trap cluster flies with sticky traps or sweep and vacuum flies when they are active. They tend to be slow and easy to crush. It is not recommended to treat wall voids with insecticides as dead flies can attract other pests such as carpet beetles. These beetles damage woolen goods and dried household items.

If many flies are emerging inside a home, try to locate the openings they are using, such as cracks behind baseboards, openings around windows, or ceiling lights. If possible, seal or mask these openings. Do not use insecticide foggers as they will not control cluster flies and may not be safe.

Although I’ve had the most questions about cluster flies, other accidental invaders that overwinter in our homes include multicolored Asian lady beetles, box elder bugs, western conifer bugs, and marbled bugs. These, too, are only overwintering and do not damage structures or people. They are managed similarly to cluster flies.

Source: Nebraska and Pennsylvania State Extension


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