These flies normally live outdoors where they occur on flowers and fruits. In late summer and fall, when the weather turns cool, cluster flies may congregate on sunny walls. They enter the home to overwinter through any available access. In the home, the flies hide, often in a cluster in attics and wall voids, in dark corners, cracks, under clothing in closets, beneath curtains, behind pictures and furniture, etc. On warm, sunny days in the winter and spring, the flies often emerge from their hiding place and swarm on windows causing great annoyance by their buzzing and by their presence. Dead flies provide a food source for larder beetle larvae and can contribute to the presence of other nuisance insects in the house. In April cluster flies lay their eggs singly in cracks in the soil. During the summer, the eggs hatch and the emerging larvae (maggots) penetrate earthworms and develop as a parasite in its host. There are several generations during the summer. The adults stop egg laying in late August and September and seek hiding places in which to overwinter. Most of the flies spend the winter outside in and on fence posts, under stones, and in other protected places. Cluster flies are usually a greater problem in rural and suburban areas due to the large grassy areas that favor high earthworm populations.

More Information and Tips on Cluster Flies Extermination / Control

• Outdoor insects that seek shelter indoors or in sheltered areas as the weather gets cooler
• Congregate in sunny areas
• Found in large numbers in sunny windows, patios, between walls, in false ceilings, basements, attics and any infrequently used areas in homes, garages, and barns
• Often worse in locations near farms
• Can number in hundreds to thousands
• Not due to unsanitary conditions
• Do not carry disease -mainly a nuisance
• Look similar to house flies but slightly larger with yellow-gold hair on thorax & gray hairs on the abdomen
• Sluggish moving
• Emit a buckwheat honey odor
• Leave a greasy, smelly residue
• Larvae found in bodies of earthworms
• Enter homes through very small numbers and usually return each year
• Often need to be treated yearly - in spring and around Labour Day
• Congregate around light fixtures and sunny windows
• All windows, doors, light fixtures, cracks and crevices treated with spray spring and early fall
• To control flies before treatment, vacuum all windows and light fixtures, empty vacuum outside and do not take refuse back into the house
• Preventative measures include caulking of all openings to prevent flies from entering your home