Last month was the arrival of the cluster flies. These flies are a bit larger than the house fly with a black/silvery-black checkered body. Young, newly emerged flies have short light-brown/yellowish hairs on their lower bodies. Sluggish movement. The cluster fly will fly around the home but at a less frantic pace than that of the house fly.
When at rest, the cluster fly will overlap its wings; the house fly's will remain separate. Clustering at windows (thus its name). If a large population exists, it will tend to cluster at windows or attics. They appear on the sunny side of the structure in heaviest concentrations in late fall and early winter, as they seek warm locations in which to live during cold months. Although cluster flies are observed buzzing and congregating at windows, screens may prove ineffective in preventing their entrance. Cluster flies are capable of crawling through small openings in the walls of a structure. They hibernate in secluded parts of houses like attics and wall voids. On sunny winter days, the wall voids become warm and the cluster flies try to move toward light. Very often they find themselves in the inhabited parts of the house and then move to the windows.
The cluster fly life cycle begins when a female lays her eggs in the soil in late summer or early fall. These eggs hatch within a few days, after which larvae seek to enter the body cavities of earthworms. Cluster fly larvae feed on earthworm hosts for several days, at which time they molt and pupate in the soil. Cluster flies’ development time from egg to adult is about 27 to 39 days.
What to do?
Fly Light Traps:
Installing insect or fly lights in attics and false ceilings is an effective approach to dealing with cluster flies when the overwintering site cannot be determined. When the cluster flies "awaken" in the spring, a fly light will attract and capture a large portion of the cluster fly population before they are able to inhabit living space.
Vacuum or swat:
Because the flies are sluggish, it is usually fairly easy to swat or vacuum those that find their way indoors. But, unfortunately, just as you get rid of these, more are likely to emerge, causing an ongoing process of swatting, vacuuming, and exasperation. I like the fly zapper that kills the fly instantly. Design like a tennis racket, it can zaps and kill several flies at a time. :)
Cluster Fly Prevention and Control:
Seal Cracks & Holes:
In early summer, before cluster flies have entered the your home, seal any visible crack or hole on the exterior with caulk. Sealing cracks during the fall or winter is not advised since it will force flies already living in wall voids to emerge on the inside of the structure. Caulk or fill all cracks and crevices in the home's structure, including:
around doors and windows.
under and in eaves and siding.
around electrical outlets.
at pipe, wire, and cable openings.
along the roof.
Apply a residual pyrethroid-based insecticide such as Suspend SC or Demon WP on the exterior of the building in late August or early September, just before adult cluster flies begin to overwinter. They will land on these surfaces and die before they can enter. These products may be applied using a one-gallon sprayer to the undersides of eaves, around doors and windows, and on the sunny side of the building.
Tip: Use yellow sodium vapor or halogen lighting outside to reduce insect attraction.
Edited by Barbara Allen