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How to Compost with Black Soldier Fly Larvae BSFL

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How to Compost with BSFL: A Beginner’s Guide

Table of Contents

Composting is a method of naturally processing food waste and yard waste into usable nutrients for your garden. While many people use composting bins and earthworms to complete this process, you should know that one type of insect is much better at composting: Black Soldier Fly Larvae.

Black soldier fly larvae (BSFL) - also known as phoenix worms, reptiworms, and calciworms in the reptile-feeding industry - are some of the most efficient composters in the world. These small maggots start out less than ⅛ of an inch and can grow to nearly a full inch long! During this time, they will eat anything - from kitchen scraps to agricultural waste like chicken and cow manure.

This article is a primer on how to raise and maintain a Black Soldier Fly Larvae composting setup. Check it out!

The Basics of BSFL Composting

The greatest thing about BSFL is that you can feed them about anything. There are very few things that they won’t eat. For instance, while citrus fruits can kill a bin of redworms, BSFL will devour limes, lemons, and oranges with ease. BSFL can also handle meat, eggs, and about any other kitchen scraps you can think of. You can also feed them chicken manure, cow manure, or any other animal scraps and they will condense it into a much more nutrient-rich substance.

Here are the basic steps you need to set up and maintain a BSFL composting process:

1. Find a Good Area to Compost

    Black soldier flies do not need a huge area, and many different setups are possible. There are several considerations that you need to take into account when choosing where your BSFL will live. 

    • BSFL are the most efficient around 80° F. If you live in a place that gets cold in the winter, you may need to store them in a garage or outbuilding with a heat lamp to keep them warm.
    • In order to keep your colony going, BSFL must turn into flies and lay more eggs. Typically, they need sunlight and temperatures above 70° F to do this. (However, there are some workarounds to these requirements, discussed below.
    • The flies are not as annoying as regular houseflies, though there will be a lot of them. Most people choose to set up their colony somewhere where they can put up insect screens to hold the flies into a given area.

    2. Start Small and Scale-Up

      You can start off by purchasing a small amount of BSFL. Start with the smallest worms (⅛”) and buy anywhere from 500 to 5000 depending on the amount of material you are trying to compost. If you are simply composting kitchen scraps you can start on the lower end, but if you are trying to process agricultural waste from a farm you can start with many more larvae.

      The reason you should start with ⅛” larvae is that this will give you plenty of time to get the conditions just right for the flies to start reproducing. While the larvae can survive and compost in a wide variety of conditions, it can be slightly challenging to get the larvae to undergo metamorphosis into flies and get the flies to lay eggs. 

      3. Induce Metamorphosis

      The key to inducing metamorphosis in BSFL is having the right conditions. When the larvae are about ¾-1” in size, they will begin looking for an area to undergo metamorphosis. Unlike the wet, hot, and humid space that is created in the compost pile, a larva undergoing metamorphosis needs a slightly drier and cooler area. When a larva is ready to undergo metamorphosis, it will enter the pupa stage. 

      You can tell that a larva is in the pupa stage when the exoskeleton turns dark brown and becomes rigid. The pupa may be able to move slightly but will be nowhere near as active as a hungry maggot. If you surround your compost pile with some dirt and wood chips, this makes a great substrate for the pupae to develop in. This process can take anywhere from a week to a month, depending on the conditions.

      After the pupa stage, long, skinny flies will emerge and begin looking for a mate.

      4. Be Prepared for Flies

        As stated above, many flies may emerge at the same time when the conditions are right. This is great because it means that you can expand your colony and keep the composting process going. However, you won’t want these flies to invade your house or the rest of your property. 

        So, just be sure that the flies will be contained to a specific area. The flies do need some room to move around, as part of their mating ritual includes the males “tackling” females out of the air. For a small colony, you will need about 12 cubic feet of space for flies to breed. Larger colonies require a larger space.

        5. Maintain the Colony

          Black soldier flies need 4 things in order to reproduce:

          • Exposure to UV light - if you cannot provide sunlight, you can buy an LED light with the appropriate wavelengths to induce breeding behaviors.
          • The right temperature - while this is not a super-specific temperature, you should keep the air temperature above 70° F and below 100° F for optimal breeding. 
          • The right humidity - Black soldier flies prefer relatively high humidity in the breeding chamber. You should aim for somewhere between 60% and 90% for optimal egg-laying.
          • A substrate to lay eggs on - typically this can just be access to the compost pile, where the flies will lay eggs. Alternatives include cardboard, wood, and other substances that sit a few centimeters above a source of nutrition (i.e. food scraps or manure).
          And that’s it! With these things in place, you should be able to turn almost all of your organic waste into dark, beautiful compost. The compost itself can be mixed directly with soil, or you can dry it out to save it for the next season. This compost - called “BSFL Frass” is extremely potent. See our page on BSFL Frass to learn the right ratios for mixing.

          1 comment

          • What’s the best way to confine adult flies? We have a barrel composter on a patio under an overhang. Was thinking about mosquito netting.

            Deborah Harvey on

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