Black soldier fly, Hermetia illucens (L.), is a true fly (order Diptera) from the family of soldier flies (Stratiomyidae). It has a considerable number of relatives in North America (about 260 described species), although most of them are not particularly remarkable and, thus, are not known to general public. Adults can most commonly be seen on flowers, where they feed on nectar. Larvae are fairly diverse in their habits: some species are predators, other species feed on a variety of decaying materials (including animal feces), while still other species feed on algae; some species are aquatic, other species live in decaying substrates, and still other species live under bark or in other concealed places. Among its relatives, the black soldier flies is the best known and the most economically important.
Like all other flies, black soldier flies have complete metamorphosis (in ento-speak, they are holometabolous). Females lay eggs, usually in a single cluster of about 600, or even more. Eggs are usually deposited in some dry protected place near a food source (e.g., in a crack in the bark of a tree right above a carcass of a dead porcupine). Larvae hatching from these eggs look like small white worms and are commonly referred to as maggots. They have absolutely no resemblance to adult flies, just as caterpillars have no resemblance to butterflies.
Newly hatched larvae colonize their food source and go through five molts, with each subsequent substage (instar) being larger than the preceding substage. Larvae are gregarious and often form large wriggling balls comprised of thousands of individuals. This helps them to maintain temperatures higher than that of the surrounding environment (insects are cold-blooded, but still generate some metabolic heat) and to better digest their food. Black soldier fly larvae have extra-oral (also known as extraintestinal) digestion. This means that they spit out digestive juices full of various enzymes, which then break down the already dead substrate that they inhabit. The larvae slurp in the resulting liquified soup. Pulling together the secretions from numerous larvae helps to release an abundance of nutrients that are shared among all of them.
The sixth instar eventually turns dark, stops feeding, and usually crawls away in search of a dry and protected place to pupate. Then it stops moving and becomes a pupa. This stage is characterized by dramatic changes in internal anatomy and external morphology and by the formation of adult organs and structures. These appear pretty much anew from groups of cells that were set aside specifically for this purpose at the larval stage.
Adults emerge from pupae and promptly take off in flight. Contrary to a common misconception, they feed on things like nectar, honeydew, bird droppings, etc. Adult black soldier flies are strong fliers; furthermore, flight is an important component of their courtship and mating behaviors. Another factor that has a strong positive effect on their mating is the presence of daylight. Insufficient light intensity or the absence of certain wavelengths from the light spectrum suppresses mating activity to the point of its complete cessation.
The rate of black soldier fly development depends on temperature, the available diet, and, to some degree, probably on humidity. When it is warm, moist, and food is nutritious and abundant, they grow the fastest. Conversely, when it is too cold or too hot, and there is not much to eat, their growth dramatically slows down. Under suitable conditions, the life cycle from egg to adult takes about 40 days. The eggs incubate for about 3−4 days. The larval stage, which as mentioned above consists of six instars, lasts for 14−22 days. Pupation is completed in 5−10 days. Adults have an average lifespan of 10 days and start mating 2−3 days after emerging from pupae.