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Larvae guide

Processing food scraps with black soldier fly larvae

Explore fast food-scrap processing with black soldier fly larvae. Plan for feeding, summer heat, the fly life cycle and finishing the residue.

Try one batch of larvae

Choose a sheltered outdoor spot and set aside somewhere to compost the residue left behind. A small feeding batch lets you try the process before taking on a breeding colony.

Black soldier fly larvae are the immature feeding stage of Hermetia illucens. They eat decaying organic material. As they mature, they darken and leave the food to pupate, the stage in which they change into adult flies. The University of Florida species guide describes the feeding stage and this transition.

Several pale black soldier fly larvae with broad, segmented bodies.
Black soldier fly larvae (Hermetia illucens), showing their broad, segmented bodies.
Photo: MD-Terraristik / Dennis Kress, Public domain.

Weigh waste reduction against colony care

Active larvae can process moist food waste, but speed depends on the feed and conditions. A controlled food-waste study found that mixed canteen leftovers supported growth while concentrated oil-separator waste caused high mortality. For a first household trial, we recommend mixed fruit and vegetable scraps, keeping bulk oil and grease out.

Poor conditions can prolong development, according to Eawag's processing guide (PDF). Survival alone does not tell you whether the batch can handle your scraps.

Buying larvae starts a feeding batch. To keep a colony going, you also need successful pupation, adult mating and egg laying. Adults need suitable light and warmth, as Eawag describes. Include the cost of replacement batches, or the care needed to breed your own larvae. A route out of the food and a dry, sheltered pupation area are part of the setup.

Measure heat inside the food layer

Eawag (PDF) gives 24 to 30°C as an ideal larval temperature range, with shaded, moist food. Excess heat drives larvae away; cold slows feeding. This is a preferred range, not a survival limit.

The food can be warmer than the surrounding air. A 2025 laboratory study measured warming that increased with larval density. Check the food layer with a temperature probe; an outdoor forecast cannot tell you its temperature.

For a Cyprus summer trial, check the location during the hottest part of the day. Provide shade, protection from rain and ventilation. If the material gets too hot, pause feeding and improve the location. Check again in cooler weather before planning a system for the whole year.

Feed a batch and follow its changes

Use the Purdue household guide for bin construction and care. Its seasonal advice is for Indiana.

  1. Choose a sheltered, accessible bin with drainage and a route for mature larvae. Prepare the separate composting space for its residue.
  2. Add a little moist starting material, such as coir (coconut fibre). Obtain an identified batch of larvae; note its arrival date and approximate quantity.
  3. Offer a small portion of mixed scraps. Adjust feeding to observed consumption: wait for the previous food to break down before adding more.
  4. Check daily during the trial. Note food added, remaining scraps, temperature, smell and care time. Keep the material moist and drain accumulated water. Persistent odour, flooding or overheating needs attention before more feeding.

For this example, assume a purchased batch in a shaded patio bin whose food layer measures 27°C. You offer 200 g of mixed vegetable scraps. At the next daily check, recognisable pieces remain, so you hold the next portion. Later, many larvae darken and head for the exit ramp. Reduce feeding as the batch matures and decide whether to finish this batch or arrange replacement larvae. These are example observations, not a timetable or feeding allowance.

Review after two weeks: compare the scraps accepted with the care time and note any larvae leaving the food. Check whether a replacement batch is needed before assuming the same feeding level can continue.

Compost the residue before using it

The material left after feeding is often called frass or residue. It may be crumbly or wet. Eawag (PDF) recommends further composting to stabilise this residue before using it as a soil amendment. Allow space and time for that stage when judging the whole process.

Follow the finishing guidance in the composting overview before putting the residue on plants.

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Sources and further reading