Cluster Flies
Everything You Need to Know About Cluster Flies
Cluster flies are usually between one quarter and three eighths inches long. They are never green or blue, but usually dark gray. They resemble house flies, except that they are usually larger, and they have a yellow color to their thorax.
The cluster fly is a parasitic fly that uses earthworms as its host. It breeds in fields and lawns, mainly during the spring months and summer months. It can be found almost anywhere in Canada and the United States, except for the Gulf States.
Female cluster flies lay their eggs mainly in soil cracks. The eggs generally hatch in about three days. The larvae use earthworms as their source of food, and they feed on them for about three weeks. Afterwards, they grow into the pupal stage, which usually lasts about two weeks. Then they emerge as adults, and feed on flowers.
When autumn nears, the cluster flies begin to make their way into structures. People have problems with cluster flies beginning in late August, as the insects move indoors to spend the winter. They are much easier to treat before they have burrowed their way as far as they can get into cracks and crevices.
Cluster flies can squeeze around the edges of weather-proofed windows. As more flies are attracted to the warmth of the building, clusters of them will gather together inside holes in walls, or in attics. They generally stay to the west or south sides of buildings, as these are warmer.
If you have a warm stretch of days in winter, the cluster flies may come out of the buildings, thinking that spring has arrived. They may fly slower when first awakened, and they are attracted to light.
To eliminate cluster flies, you can spray into the voids around windows where they stay for the winter. But your house has many voids that they know about and you don't. Inspect cracks on the western and southern sides of your house. You can use a dirt devil or other small vacuum to get rid of any bugs you can see, if you don't want to use a bug spray.
It's easier to prevent their intrusion that to get rid of them. In August, use a repellent spray where they are likely to land to enter your home. Apply to eaves, soffits, door frames and window frames, and any other areas that look like the cluster flies could get in. You can also use an insect dust to puff into the areas that the cluster flies may be drawn too. This may help keep them from moving in. Prepare your home ahead of time, and you won't have to share it with cluster flies in the fall and winter months.