How to Compost with Black Soldier Fly Larvae

If you've ever watched a pile of food scraps sit in a bin for months barely changing, you already know the frustration of traditional composting. Black soldier fly larvae (BSFL) do something different. They eat fast, break down almost anything organic, and leave behind a nutrient-dense output that your garden will love — all in a fraction of the time.

This guide covers everything you need to know about BSFL composting: what it is, how it works, what you can and can't compost, and how to get started.

What Is BSFL Composting?

BSFL composting — also called bioconversion — is the process of using black soldier fly larvae (*Hermetia illucens*) to break down organic waste. The larvae are voracious feeders during their growth stage (3rd–5th instar), capable of consuming roughly 10–15% of their body weight in organic matter every single day.

Unlike traditional hot composting or worm bins, BSFL bioconversion doesn't require turning, doesn't produce the same odors (when managed correctly), and processes material significantly faster.

The larvae aren't pests. Adult black soldier flies don't bite, don't feed, and aren't attracted to your home in the way houseflies are. They're a beneficial saprophyte — nature's waste processor.

What Can You Compost with BSFL?

One of the biggest advantages over worm composting is the range of materials BSFL will process. They readily eat:

- Fruit and vegetable scraps

- Coffee grounds and tea leaves

- Cooked food waste (including some dairy and meat in small quantities)

- Spent grains from brewing

- Manure (chicken, rabbit, cow, pig)

- Pre-consumer food prep waste

- Cardboard and paper (in smaller amounts mixed with wet material)

Avoid or limit:

- Large volumes of meat or fish (pathogen risk, pest attraction)

- Heavily salted or acidic foods (disrupts the microbial environment)

- Onions and citrus in excess (can slow feeding)

- Pesticide-treated produce (larvae bioaccumulate toxins)

- Anything inorganic — plastics, metals, treated wood

The practical takeaway: your kitchen scraps, coffee grounds, fruit, veg, and most food prep waste are perfect. BSFL handle the things worm bins can't.

How Fast Does It Work?

At optimal temperatures (27–30°C / 80–86°F), larvae in their peak feeding stage can reduce organic waste by 50–75% in 10–14 days. The remaining material — called frass — is a combination of larval castings, shed exoskeletons (chitin), and partially digested substrate.

Factors that affect speed:

- Temperature: Below 24°C (75°F) feeding slows significantly. Below 20°C it nearly stops.

- Moisture: Substrate should be 60–70% moisture by weight — clumps when squeezed, doesn't drip.

- Stocking density: Too few larvae relative to feed volume means slow processing. Too many and you get overcrowding and heat spikes.

- Feedstock variety: A varied diet processes faster than a single material. Mix dry and wet inputs.

What Do You Get Out of BSFL Composting?

Two things: prepupae and frass.

Prepupae are the larvae in their final stage before pupation. They're dark brown, plump, and packed with protein and fat. If you're raising chickens, reptiles, fish, or other livestock, prepupae are a high-value live or dried feed. This is one of the key reasons BSFL bioconversion is gaining traction with backyard farmers — it converts waste into feed.

Frass is the composted output left after the larvae migrate out. It contains:

- Nitrogen, phosphorus, and potassium from the breakdown process

- Chitin — a compound that stimulates plant immune responses and suppresses certain soil pathogens

- Beneficial microbial communities

- A lower pathogen load than raw manure inputs

Frass can be applied directly as a soil amendment, worked into planting mixes, or top-dressed around established plants. It's a genuinely useful fertilizer, not just a waste byproduct.

How to Get Started with BSFL Composting

You don't need a complex setup to begin. Here's the short version:

1. Get a bin with a self-harvesting ramp.

Prepupae are photophobic and will naturally migrate away from the feeding zone when they're ready to pupate. A bin with a ramp lets them self-harvest into a collection container. This is the single most time-saving design feature. Our BSFL Bin Kit is built exactly for this — everything you need to get started in one package.

2. Source your larvae or eggs.

You can buy starter larvae or eggs from suppliers like Blue Grub Farms, or collect wild pupae during summer months if you're in a region where BSF are present outdoors (May–September in Colorado and most of the continental US).

3. Set up your environment.

Larvae need warmth. Optimal range is 25–35°C (77–95°F). If you're keeping your bin indoors in a climate-controlled space, most homes during summer are adequate. Winter indoor temps need monitoring — if your bin is in an unheated garage, activity will drop significantly.

4. Start feeding.

Add food scraps gradually at first. As your colony grows, scale up. The larvae will regulate themselves — if there's too much food, it will smell; too little, and they'll slow down. You'll get a feel for the rhythm quickly.

5. Harvest prepupae and frass.

When larvae begin darkening and migrating up the ramp, collect them. What's left in the bin is your frass.

Frequently Asked Questions

Does BSFL composting smell?

Managed properly, no — or very little. The main odor causes are substrate that's too wet (anaerobic decomposition) and overfeeding. Both are easy to correct. An active BSFL bin smells earthy at most.

Will it attract flies or pests?

Black soldier fly larvae actually outcompete houseflies and many other insects for food resources. A healthy BSFL bin is one of the better defenses against housefly populations in a composting area. That said, covered bins reduce pest attraction generally.

Can I compost meat and dairy with BSFL?

In small amounts, yes. Unlike worm bins, BSFL handle these without significant issues. Large quantities of meat increase pathogen risk and can attract rodents — keep it balanced.

How many larvae do I need to process my household waste?

A small household generating 1–2 lbs of food scraps per day can be managed with a colony of a few thousand larvae. The bin kit comes with a starter culture sized for typical household waste volumes.

Do I need to maintain the colony year-round?

If you're in a cold climate, you'll need supplemental heat in winter to keep the colony active. Some people let the colony wind down in winter and restart in spring — it depends on whether you have a consistent source of prepupae to feed animals.