Table of Contents

How to Breed Black Soldier Fly Larvae

Table of Contents

Black Soldier Fly Larvae (BSFL) are one of the world’s best composting insects. They can easily turn all types of food waste and agricultural waste into clean, nutrient-dense compost. Plus, they can serve as a valuable feed insect for livestock, reptiles, and invertebrate pets. If you do it right, BSFL composting can even become an extra source of income.

In this article, we are going to dive into the specifics of how to breed black soldier flies and create a fully operational larvae and compost production facility. If you are new to BSFL composting, be sure to start with our Beginner’s Guide. Let’s dive right in!

Black Soldier Fly Life Cycle

Egg to Maggot

Like all insects, Black Soldier Fly Larvae start life as an egg. Hatching with nearly 500 brothers and sisters, a black soldier fly maggot is only about 1 mm long at birth. Over a period of about 2 weeks, this maggot will go through several “instars” - sort of like phases of larval growth. Though the first instars are only about 1mm, the last instar can be ¾” to 1” long. Compared to other composting organisms (such as redworms), this is a MASSIVE growth rate. To grow this fast, the maggots need a huge amount of energy. When thousands of worms are working together, BSFL become some of the fastest and most efficient composters on the planet!

Maggot to Pupa

After molting into the final instar phase, the maggot will eat just enough to grow a little larger and store energy as fat. It will need this energy to go through the next phase of its life - the pupa stage. BSFL that are ready to enter the pupa stage will leave the compost pile (a fact that can be utilized to collect the worms, see below). These larvae seek a dryer, cool, dark area where they can complete the process of metamorphosis. When they find the right spot, the exoskeleton becomes darker and more rigid. A pupating maggot will hardly move. After a period of about 2 weeks in the pupa stage, an adult fly will emerge.

Pupa to Adult Flies

Adult black soldier flies are very different than common houseflies. They have an elongated body, with a clear section of exoskeleton on the medial portion of their abdomen. It is thought that this elongated body and the clear section on their abdomen are meant to mimic the shape of a wasp, potentially scaring predators away. While the flies may mimic wasps in appearance, they certainly do not mimic their aggressive behavior. Black soldier flies are extremely docile, and they move so slow that you can typically pick them up with your thumb and forefinger without them flying away. Since these adult flies only have about 4-5 days to live, they tend to wait for just the right time to find a mate and reproduce. 

Mating to Eggs

To find a mate, black soldier flies engage in ritualistic mating behavior. They fly high in the air, typically above or near a good source of compost that can serve as food for their young. The females dart around and it is up to the males to “tackle” a female in midair. If the male can successfully grab a female and start the copulation process, the female will submit. The two will remain “butt-to-butt” as the male transfers sperm to the female. This process can last anywhere between a few minutes and an hour. 

The sperm fertilizes eggs in the female, and she will begin looking for a spot to lay her eggs. Typically, female black soldier flies prefer wood, cardboard, corncobs, and other surfaces that have small holes. The female will back her abdomen into the hole and deposit up to 500 eggs at a time. These eggs are about 1mm each, and they will hatch after several days. This starts the cycle over. Since each female lays so many eggs, the maggots can increase exponentially from generation to generation. 

Setting Up a BSFL Composting Bin

While you can simply introduce BSFL to any composting heap, there is a particular bin design that can help you more easily maintain the colony and harvest the largest black soldier flies. This design will allow you to harvest mature larvae easily, without having to sort them out of the compost itself. It relies on the fact that mature black soldier fly larvae will leave the compost to seek a safe place to pupate.

BSFL Bin Design

The perfect black soldier fly larvae composting bin has a square bottom and sides that form small ramps. The angle of the sides should be slightly less than 45°, which will allow the black soldier flies to climb out of the compost when they are ready. To collect these worms, you can attach a PVC pipe (cut in half lengthwise). These half-pipes can have holes cut at various intervals which allow the worms to fall through. Attach a small bucket or jar below the holes, and the worms will self-harvest. Save some of the worms and allow them to pupate into adults, while you can feed the rest to your chickens.

Add new compostable materials directly on top of the currently composting material, until the bin starts to become full. The maggots will greatly reduce the volume of the material you add. You may be surprised how much material you can add to a bin before it becomes full of nutrient-rich compost. To harvest the compost, follow the next step.

Rotate Compost Bins

Allow flies to breed and lay eggs in the compost bin. You can accomplish this by screening in the compost bin (while making sure to meet the environmental variables below). This will add new worms and keep the composting happing as efficiently as possible. When your bin starts to get full, do not allow any more flies to access the bin. The remaining worms will continue composting until they reach full size. Once all the worms have grown up and you are no longer harvesting worms, the compost is ready to be used.

When you stop adding new material to the compost bin, you will need to start a second compost bin. Allow the adult flies to access this compost bin, and a new generation of worms will begin composting this material. If you add a little of the compost from the first bin, it will encourage the female flies to lay their eggs in the new bin. Repeat this cycle, alternating between bins to successfully produce massive amounts of compost that is free of worms. 

What to Compost (BSFL Food Supply)

BSFL can survive on an amazingly high variety of foods. Unlike redworms (which can be killed by citrus, meat products, eggs, and other foods), black soldier fly larvae thrive on almost any organic, energy-rich substance. There are a few things which they will not be able to eat, such as the hard rinds of fruits like lemon peels, orange peels, and avocado skins. Though they love to eat corn kernels, they will not be able to fully compost corn cobs simply because they are too hard and dry. If you are simply composting your kitchen scraps, there is almost nothing that the maggots won’t try it eat. As long as the foods you give them are pesticide-free, there is very little from a home kitchen that can harm a BSFL composting operation.

On a more commercial and agricultural scale, black soldier flies are very adaptable. Many farmers successfully use BSFL to compost agricultural wastes - from manure to spoiled feed to waste products from the harvest process. BSFL can easily convert manure from almost any animal into a much more nutrient-dense compost. This can greatly increase your feed-conversion-ratio by adding value to the waste products that animals produce and feeding the larvae back to chickens, fish, and pigs. (BSFL can also become an additive for other animals if they are processed right.) BSFL can also process production waste, such as fish guts, almond husks, and the stalks and leaves of many crops that are otherwise not valuable. 

Creating an Environment for BSFL

Black soldier flies live naturally in several parts of the southern United States where the temperature and humidity stay at appropriate levels throughout the spring, summer, and fall. However, if you live in areas outside of the southern states, you may need to adjust your setup a little to create the right conditions for the flies.

Temperature

While black soldier flies can tolerate a range of temperatures, they are typically most efficient at around 86° F. You may need to add a heat lamp on a thermostat to ensure that the air temperature above the compost bin remains close to this temperature. If the temperature starts to reach the high 90s, you may need to add a fan or move the compost bins into a cooler, shaded area to ensure that they do not overheat. While the maggots can tolerate fairly high temperatures, they will start to die off if the temperatures reach above 100° F. 

Humidity

Similar to temperature, BSFL can tolerate a range of humidities. Inside a compost heap, there is typically plenty of water as the compost is created. If temperatures are not too high, evaporation from the compost bin will happen at a slow rate and the addition of new foods can ensure the maggots have enough moisture to thrive. 

As for the adult flies, they do best at around 70% humidity, give or take about 10%. Certain areas of the country naturally have enough humidity in the air to sustain these flies. In very dry states, you may need to add a humidifier to the room or chamber you are composting in. You will know when the humidity and temperature are right because the flies will become more active and will start seeking mates, mating, and laying eggs.

Lighting (UV especially)

Black soldier flies have a need for UV light to properly develop their eggs. In fact, without UV light, the flies will not even try to mate. If you are composting outdoors, this is no problem. The sun provides a full spectrum of light, so all of the spectrums the flies need are provided. If you are composting indoors (like a garage or an outbuilding) you will need to add an artificial light source. Scientists have found that the best artificial source is an LED light made with specific diodes. These diodes emit UV light, green light, and white light to get a good mix of wavelengths that can stimulate black soldier fly production. Evo Conversion Systems makes a variety of black soldier fly LED lights for different sized operations that seem to work well. 

Utilizing BSFL Compost (Frass)

Compost created by black soldier flies is actually so nutrient-dense that it could kill plants if applied at full strength. There are several ways to utilize the compost created from black soldier flies that decrease the concentration, makes the compost last longer, and provides your plants with the perfect balance of nutrients and minerals. Here are a few ways it can be used:

• Dried Frass: Dry out the compost and crush or grind it up into small granules. These can be sprinkled on the surface of the soil and will slowly leach their nutrients into the soil when you water or when it rains. Start with a test area, since these granules can be much more concentrated than you expect. If your plants show signs of “burning” (blackened leaf tips), you need to reduce the amount of dried frass that you use.
  
  
• Frass “tea”: By mixing the frass directly into water, you can create a liquid nutrient broth that you can spray directly onto plants. You may have to do some experimentation with each batch of compost that you make, given that each food source can impart different nutrient compositions to the compost. Once you let the tea steep for a day or so, the particulate matter can be filtered off and you can add the nutrient broth to a sprayer to cover large areas.
  
  
• Mixing directly with topsoil: By mixing the compost directly with nutrient-poor soils, you can create a perfect planting / potting mix that will feed your plants for months. If you start with spent topsoil, add some BSFL frass and some vermiculite to lighten the soil, and mix it all together well, you will have a great all-around planting mix that can be used for indoor plants or for creating a new garden bed.