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Phorid flies are common indoor insect pests that can be identified fairly easily on account of their seemingly odd behaviors and distinct physical features. Phorid flies are relatively small flies that closely resemble fruit flies, but phorid flies do not have the unique red eyes that make fruit flies unique. Phorid flies can also be recognized by their erratic manner of flying, and if these flies are approached while they are in contact with surfaces they will not fly away as would be expected; instead, phorid flies will rapidly run from humans and other threats in much the same way as any terrestrial arthropods would.

Indoor phorid flies rapidly establish nuisance infestations after gaining access into homes, as females are able to lay around 500 eggs during their short lifespan. Females lay around 40 eggs within a 12 hour period, and larvae emerge after 24 hours. Eggs are deposited on decaying organic matter, and if eggs are laid within warm and moist conditions they will develop into adult flies in as little as 14 days, but the maturation process can take as long as 37 days if development occurs within less than ideal cool and dry conditions. Infestations can only occur in areas where breeding sites are abundant. The most common breeding sites include fermenting fruits, garbage containers, rotten vegetables, improperly stored meats, and containers that contain moist foods. Organic-based glues and paints also serve as a breeding site.

These flies often become abundant within homes where these common breeding sites cannot be found, which may perplex residents struggling to control an infestation. In these cases, phorid flies are likely breeding in drains that contain organic buildup, which is why these fly pests are often referred to as “drain flies.” It is not uncommon for large numbers of these flies to enter homes that are located near outdoor breeding sites, such as dumpsters, residential garbage cans and recycle bins. Eradicating indoor infestations are particularly difficult when the fly pests breed within wall voids where mold and/or fungal organisms have formed due to high-moisture conditions and/or plumbing leaks.

Have you ever lived in a home that became infested with phorid flies?