Cluster Flies!

We all hate when the occasional fly gets in our home during the summer.  But, there's another fly that makes it's appearance in homes and buildings in late fall.  It is the cluster fly, also called the attic fly.  They can be found gathering in clusters on the sunny side of buildings in the fall looking for shelter for the winter.



Cluster Fly; photo courtesy of wiki.bugwood.org

Cluster flies are slightly larger than the common housefly.  They are gray in color with light and dark gray checkered abdomens.  They have golden yellow hairs on the thorax.  Cluster flies are slower and more sluggish than your common fly.

Although they can be a nuisance because of the large numbers that cluster together, they are not known to carry any diseases that are of medical importance to humans.  They do not reproduce inside the structure.  They may be seen in large numbers, however, on warm days trying to get back outside.  They are attracted to light and are often found clustered around window frames.



Flies around window; photo courtesy of www.ecopro.co.uk

In the spring, cluster flies will emerge to start their life cycle again.  Eggs are deposited on soil where the larva use earthworms as their hosts.  They will develop as parasites in the worm and pupate into adult flies.

As with all fall pests, prevention is the best treatment.  To keep them out, seal cracks around windows, doors, siding, pipes, and other openings.  Repair or replace damaged screens on doors or windows.