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The time of year that sees the greatest amount of indoor cluster fly infestations is fast approaching. Cluster flies are well distributed in North America, especially in such regions as the upper-midwest, the northeast and southeast Canada. Although cluster flies do not inflict bites on humans and are not disease-vectors, these flies are notorious for causing major nuisance infestations within homes and buildings during the summer and fall seasons.

Cluster flies belong to the Pollenia genus and they get their common name from their habit of clustering into a large mass on walls inside of homes. Cluster flies also infest hard-to-access areas of a home like wall-voids, beneath floorboards, and within attics. These flies gravitate into homes in the northeast during the late summer and fall seasons where they will remain until the spring season arrives unless the flies are professionally eradicated. Like most indoor fly infestations, cluster flies are extremely difficult to eradicate from a home, which is why many residents of the northeast take measures to prevent the flies from entering their home.

Cluster flies are masters at squeezing into homes through narrow and well-hidden cracks and openings. This is why some residents take time during the summer season to seal all cracks and openings around their home. Although cluster flies are well known insect pests, scientific information concerning the Pollenia genus is scarce. In fact, up until recently, all cluster flies were referred to as one species, Pollenia rudis. As it turns out, there exists at least six cluster fly species that are known for invading homes in the northeast.

The Pollenia labialis species is most abundant within homes during the month of July, but this species is not as abundant in the northeast as the relatively small Pollenia griseotomentosa species, which infests homes in the region between April and October. The Pollenia vagabunda species was most likely introduced into the US from Europe, but this species is not as troublesome for homeowners in the northeast as the Pollenia pediculata and Pollenia rudis species. These two species are responsible for establishing the vast majority of cluster fly infestations within homes and buildings all over the US.

Have you ever found a large amount of dead flies in any areas of your home?