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Where Do Massive Cluster Fly Swarms Disappear To Within Arizona Homes During The Fall And Winter? Will The Flies Reemerge Unexpectedly At Some Point?

Many fly pest species that closely resemble domestic houseflies are well established throughout the United States, and many of these species spread numerous disease-causing microorganisms. A large number of fly pests, such as stable flies, horse flies and deer flies, inflict painful bites to humans, but luckily, biting fly pests rarely establish indoor infestations. However, indoor fly pest issues are by no means uncommon anywhere in the US, especially Arizona. Unfortunately, many of the most common indoor fly pest species, including domestic house flies, blowflies and fruit flies, acquire dozens of dangerous pathogens from decaying organic matter in outdoor environments before entering homes where they may contaminate human food sources and indoor surfaces. Despite their filthy breeding, feeding and nesting habits, indoor fly pests rarely transmit pathogens to humans, but they can become a tremendous nuisance to homeowners, especially in Arizona where the climate allows fly pests to remain active all year round. One of the most common nuisance fly pest species, Pollenia rudis, is one of the few fly species that invades homes in large numbers in order to overwinter.

rudis is more commonly known as the “cluster fly,” or “attic fly” due to this species’ habit of clustering within obscure and hard-to-access indoor areas, particularly attic spaces. P. rudis is a type of blowfly, and although this species is traditionally regarded as the definitive cluster fly species, many other blow fly pest species in Arizona and elsewhere have become known by this common name. Cluster flies can invade homes during any time of year in the southwest, but they tend to swarm indoors during the fall and winter seasons in response to dropping temperatures. These fly pests often cluster in overwhelming numbers on the exterior walls of houses, especially in areas that are most heavily exposed to sunlight. After gaining access indoors through small cracks, crevices, attic vents and other exterior entry points, cluster flies tend to gather in wall voids and other inaccessible areas before entering a state of dormancy for the winter. Once spring arrives, the flies naturally emerge from their indoor refuges in order to swarm back outdoors, resulting in unexpected nuisance swarms within homes, often on unseasonably warm winter days. Liberal amounts of soil insecticide effectively eliminate cluster fly larvae before they emerge as adults.

Have you ever witnessed flies swarming near residential structures?

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