One of the strangest insects encountered around the home is the soldier fly, or stratiomyid fly. The larval form of this insect is a segmented, maggot-like creature, that can be quite alarming to the uninitiated.

The most common species of soldier fly, Hermetia illucens, is commonly considered a filth fly because of its habit of breeding in manure and garbage. However, the feeding habits of this insect are not easy to classify.

The immature (larval or maggot) stage of the soldier fly feeds on decaying organic material including manure and very moist, rotting vegetable matter. In manure piles these insects are sometimes considered beneficial because they prey on other insects, like house flies. Occasionally, they may infest animal carcasses and are commonly found in and around compost. Infestations in homes sometimes occur following the extermination of a bee nest inside a wall void or other inaccessible site, where the larvae feed on waste materials in bee combs.

Soldier flies are most commonly seen in homes during their "pre-pupal stage". Pre-pupal larvae are fully grown immatures that have stopped feeding and begin a wandering behavior in preparation for pupation (the process of changing into an adult, or in this case the fly, form). During this wandering phase, larvae may travel several yards from the breeding site, and may be seen wriggling along a floor, patio, or fireplace hearth. Soldier fly larvae are about one inch-long, legless, dark brown in color, and flattened. The "skin" has a distinctive, leathery texture.

The adult stage of the most common species of soldier fly is about 3/4 inch-long and black, with a translucent segment on the tail, or abdomen. Adult flies are rather sluggish until induced to fly. They may be attracted to light, but do not seem to bother food.

Are they Bad? Soldier flies are harmless to people, and serve a beneficial role in helping decompose garbage and filth, and even control more noxious insect pests, like house flies. However, their presence in a home is usually undesirable and may be a symptom of an unsanitary situation.

Poorly maintained compost piles; spilled, wet grain; or other decaying vegetable material may provide breeding sites for soldier flies. A dead bird or rodent in an attic or chimney may also be the reason for soldier fly or blow fly infestations. Bee nests that have been allowed to live in a wall void or eave of a home can also be a source of these pests.

Control. The best control is to locate and eliminate the breeding source. The larvae themselves are harmless and can be picked up by hand, or with a tissue, and discarded. Adult soldier flies can be killed with a fly swatter. If flies become numerous, an aerosol insect spray containing pyrethrins will readily kill the adults.