Cluster Fly Facts & Information

You’re probably used to swatting flies in the kitchen during the summer months. However, cluster flies make their debut in the autumn when they fly to the sunny sides of homes in search of protection from the coming winter months. Cluster flies can be found flying about inside, often in great numbers, throughout the winter. These flies are not reproducing within the structure, but become active on warm days and crawl out of wall voids and attics in a confused attempt to go back outside. Like any fly, they can fly in through open doors, tears in screens, as well as cracks and crevices in walls and foundations.

The adults leave their protected over-wintering sites in the spring and will lay eggs on the soil, which contains earthworms. The hatching larvae enter earthworms, develop to their last larval stage, pupate and emerge as adults to begin the cycle all over again. With the onset of autumn, the current crop of adults will seek protected over-wintering sites like hedge rows, under the bark of dead and dying trees, in the crevices of south-facing cliffs and rock faces, and within the cracks, crevices and voids in sheds, garages, barns, and houses.

As a nuisance pest, they join the ranks of other over-wintering pests such as the stink bug and the boxelder bug. Cluster flies will not damage your home. Occasionally, the flies may leave small dark-colored spots of excrement on windows and walls, but they are not known to carry any diseases of medical importance to humans. In addition to the ‘clustering’ on the sunny exterior of buildings in the fall, the flies will gather in large numbers at windows within the home on warm winter days. The flies are typically sluggish in flight and can be easily swatted or captured.

While they do not spread bacteria, bite, or lay eggs in food cluster flies can be a serious nuisance and will seek out your home or business for over-wintering. It’s very common to find them in a loft, in sunken spot lighting, or under insulating felt layers. Cluster flies will also return year after year unless you take the necessary steps to keep them out. There are some fly treatments we can provide but fly control truly comes from education and sanitation changes/strategies. Our trained technicians can teach you all of them!

Professional exclusion services are the best method to keep cluster flies from entering your home. Cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the fascia and other openings should be sealed with good quality silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced. If numerous flies are entering the living areas of the home, attempt to locate the openings where the insects gain access. Typically, flies will emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. Seal these openings with caulk or other suitable materials to prevent the insects from crawling out.

We’re passionate about helping you control flies in your home because we live and work here – it’s our neighborhood, too. With our 130 years of experience keeping homes and businesses in Massachusetts, Connecticut, New York, Maine, Vermont, New Hampshire, and Rhode Island safe from pests, Waltham has the experience you can trust.