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Flies belonging to the Phoridae family are common indoor insect pests that are often referred to as phorid flies, scuttle flies, coffin flies or humpback flies. More than 3,500 of these flies have been documented worldwide, only two of which are common house pests in the US. These flies can be recognized for their habit of running along horizontal and vertical surfaces in cases where most other flies would simply become airborne. Even when these flies are approached by humans, they tend to run away rather than fly, and they are relatively small at ⅛ of an inch in length. Their yellow or light brown color also distinguishes phorid flies from other common indoor fly pests, such as houseflies, fruit flies, cluster flies and drain flies.

Phorid flies feed and deposit eggs on a variety of indoor foods and decaying organic matter. While most residents would likely insist that their home does not contain decaying organic matter, they would be wrong. For example, indoor garbage cans are the most obvious source of decaying organic matter within a home, and drains, such as sink drains, particularly garbage disposals, provide phorid flies with a rich source of rotting food. When phorid flies establish indoor infestation, residents should remove all garbage and clean drains with a corrosive solution. However, when phorid flies become abundant within a home where no source of decaying organic matter can be found, there is a good chance that they arrived indoors from the sewer as a result of broken or cracked sewer lines beneath a home. While such an event may seem rare, broken sewer lines are a common source of indoor phorid fly infestations.

The gradual settling of ground soil and invading tree roots are the two most common ways in which residential sewer lines break. When this occurs, hundreds or thousands of pounds of organic material (human waste) can absorb into the soil beneath a home’s foundation and concrete slab. Phorid flies will establish a permanent presence around a home. The only way infestations such as these can be eradicated is by fixing the sewer line.

Have you ever experienced household insect issues as a result of septic breakages or defects?