What Is a Black Soldier Fly?
The Black Soldier Fly (Hermetia illucens) is a non-pest fly in the family Stratiomyidae. Adults are about 15–20mm long, dark-colored, and often mistaken for wasps due to their body shape, though they have no stinger and cannot bite. Adult flies don't eat solid food. Their sole purpose as adults is to mate and lay eggs; they live 5–14 days in typical conditions, fueled entirely by fat reserves built up during the larval stage.
Unlike houseflies, Black Soldier Flies are not attracted to human food, do not regurgitate on surfaces, and are not considered sanitation risks. Entomologists classify them as beneficial insects because their larvae process organic waste more efficiently than nearly any other decomposer.
What Do the Larvae Do?
BSFL eat organic waste, fruit and vegetable scraps, coffee grounds, grain products, eggshells, and convert it into protein-rich biomass. A single larva can consume several times its body weight in food waste over its 2–3 week larval stage. At the end of that stage, larvae become prepupae and migrate out of the food source instinctively, which makes them easy to harvest.
What makes BSFL unusual among decomposers is the quality of what they produce. Their bodies at harvest contain roughly 40% protein and are exceptionally high in calcium, with a calcium-to-phosphorus ratio of approximately 1.5:1, close to the ideal 2:1 ratio for most reptiles. Their frass (the material left behind after feeding) is a nitrogen-rich soil amendment with significant amounts of chitin, which has documented benefits for soil health and plant disease resistance.
Who Raises BSFL and Why?
Reptile owners use larvae as a feeder insect. BSFL are accepted by bearded dragons, leopard geckos, chameleons, and most other insectivorous reptiles. Because of their favorable calcium-to-phosphorus ratio, they reduce or eliminate the need for calcium supplementation (dusting) that crickets and mealworms typically require.
Backyard poultry keepers feed BSFL to chickens, ducks, and other birds as a high-protein, high-calcium treat. If you've never tossed a handful of grubs into a chicken run, you're missing out on pure chaos in the best way possible. Birds go absolutely nuts for them. BSFL are one of the few treats that actually improve the flock's nutrition instead of diluting it, and the calcium content supports strong eggshells without extra supplementation.
Home composters use BSFL to process kitchen scraps faster and more completely than traditional compost bins. A small colony can process a household's food waste continuously, and the resulting frass is ready to use in the garden.
Hobbyist insect farmers raise BSFL as an introduction to insect agriculture, a growing field with applications in animal feed, soil amendment, and waste reduction at commercial scale.
The BSFL Life Cycle
The full lifecycle from egg to adult fly takes approximately 5–6 weeks under warm conditions (around 27–30°C / 80–86°F):
Egg: Females lay 500–900 eggs in dry crevices near a food source. Eggs hatch in 3–5 days.
Larval stage: Larvae feed and grow for 2–3 weeks, passing through several instars. This is the stage most people interact with, the larvae are cream-colored, about 20–25mm at full size, and visibly active when feeding.
Prepupal stage: Larvae stop eating, darken, and migrate away from the food source. This is the self-harvesting behavior that makes BSFL easy to collect, ramps or exit tubes capture them automatically.
Pupal stage: Larvae pupate over 10–14 days.
Adult: Flies emerge, mate, lay eggs, and die within 5–14 days.
Are BSFL the Same as Maggots?
Technically, "maggot" refers to any fly larva. But the word carries associations with housefly larvae, disease, and decay that don't apply to BSFL. Black Soldier Fly Larvae are raised in clean conditions on food-grade substrates, not on rotting waste or carcasses. We don't use the word, we call them larvae, grubs, or BSFL.
Are BSFL Available to Buy?
Yes. Dried BSFL are sold as a feeder and as a supplement in many pet stores and online. Live larvae are harder to find commercially but can be raised at home with a basic setup. The Blue Grub Farms Bin Kit is designed specifically for first-time BSFL growers, it includes everything needed to start a colony from scratch.
Frequently Asked Questions
Do Black Soldier Flies bite?
No. Adult Black Soldier Flies have no functional mouthparts for biting or stinging. Larvae also do not bite humans.
Are Black Soldier Flies a pest?
No. They are classified as beneficial insects. Adults don't enter homes seeking food, don't damage structures, and are not disease vectors. Larvae only appear where organic waste is present, they don't infest clean environments.
Do BSFL smell?
A well-managed BSFL bin has a mild earthy smell, similar to a healthy compost pile. Poor airflow, too much moisture, or overfeeding can cause odor. A properly maintained bin is not objectionable to most people.
Where do Black Soldier Flies live naturally?
Hermetia illucens is native to the Americas but has spread globally through trade and is now found across most tropical and subtropical regions. In North America it is common throughout the southern and western United States, including Colorado.
