Often confused with the common house fly, cluster flies are a common sight in most households during colder months. Like boxelder bugs, they are most active in the fall, where they can usually be found sunning on the southwest side of buildings. Cluster flies will look for places to enter your home to spend the winter. Often they will come out of their winter hibernation on warmer days. On these days they frequently appear around windows, as they are looking for a way to get back outside. They are typically still sluggish at this time, and therefore are easy to capture or swat.
Unlike other members of the blow flies family, cluster flies do not eat or lay their eggs on dead animals. Their main source of food is actually earthworms. Cluster flies will breed during warm weather, and lay their eggs in soil. Once the eggs hatch the larvae will burrow into the ground and feed on earthworms. They will then pupate, and emerge as fully-grown flies. This process can happen multiple times per year as long as the female cluster fly has adequate food.