Stable flies are common biting insects that feed on the blood of humans and many animals. These flies pose a threat to humans in outdoor environments where they tend to bite ankles, and their mouthparts easily penetrate socks and stockings. While stable flies rarely become pests within homes, the false stable fly (Muscina stabulans) is one of the most common indoor fly pests, and their habit of laying eggs on indoor food sources is well known for causing a serious intestinal disease known as myiasis. When humans eat food that is contaminated with the eggs and larvae of false stable flies, myiasis is likely to result. This disease is spread by numerous fly species, but the false stable fly is believed to spread the disease more often than any other indoor fly pest.

The false stable fly is more closely related to the common house fly than the stable fly, and their appearance is largely the same, only house flies are slightly smaller in body size. False stable flies lay eggs in feces, ripe or rotting vegetables, and lawn clippings. A large number of larvae can develop into adults on extremely small bits of dead grass, as one documented incident saw 25 adult stable flies emerge from a chunk of dried grass located on the blade guard of a lawn mower. Females frequently invade homes in order to lay hundreds of eggs over a variety of food sources. Eating food sources that are contaminated with this species’ eggs and larvae is the leading cause of intestinal myiasis.

In addition to false stable flies, another closely related species, Muscina assimilis, is also associated with myiasis. Muscina assimilis is darker in color than the false stable fly, and their legs are entirely black, while the legs of the false stable fly are reddish-brown. Muscina assimilis becomes a pest within homes less frequently than false stable flies, and the former is not nearly as abundant as the latter in the northeast.

Have you ever found fly pests in your home that were not common house flies?