“We keep finding these odd-looking creatures crawling around on the floor. We only see one or two at a time, but we have been seeing them for several weeks now. This happened last summer as well. What are these things and where are they coming from?”
These are black solder fly larvae. Once they are fully grown the larvae usually crawl away from their breeding site in search of a dry, secure place to pupate, and this is when they are most often seen. They can crawl some distance at this time, so the actual breeding site may be several yards away, possibly even outside. You may also be seeing some black, wasp-like insects flying around the house? These are the adult flies, which are often mistaken for wasps.
Black soldier flies are commonly seen in agricultural settings, where they breed in a wide range of decaying organic matter, including animal waste, dead animals, wet feed products, decaying plant material, decaying grain products and similar items. Although they are less common in household settings, these filth-breeding flies can occur in and around houses anytime they find a suitable breeding source.
A crack or breach in the septic system is one possible source of such an infestation. This could include problems such as broken wax seals under toilets, breaks in slabs and plumbing, or sewage problems immediately outside the house. Another possibility is that soldier flies are breeding in some type of decaying organic matter immediately outside the house, items such as pet feces or wet pet food or bird seed, and some of the wandering larvae are crawling up the foundation and into the house as they search for pupation sites. Yet another possibility is that they are breeding inside the house in some type of moist, decaying organic matter, such as pet feces, carcasses of small animals or birds (these may be in an attic, crawl space or wall void), misplaced open containers of canned pet food or lost food items (the dog filched that steak you were thawing out last month and hid it in the house).
Soldier flies are sometimes grown intentionally. Several companies are using soldier flies to convert animal waste products, such as catfish or poultry offal, into pet and animal feed. They use the wandering habit of the full grown larvae to facilitate collection of the insects, which are then dried and processed into meal and other products. According to product labels, meal made from dried black soldier fly larvae contains approximately 40% protein, 15% fat, and 8% fiber. There are even efforts to utilize soldier flies in products developed for human consumption.
Control: Insecticides are rarely useful for soldier fly control. Control depends on finding and eliminating the breeding source and/or improved exclusion. Often this is as simple as finding and removing a single item, like that steak the dog hid, but at other times control can be more costly, involving things like extensive repair to the septic system.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service. The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
Mississippi State University is an equal opportunity institution.