On average, a female black soldier fly lays around 500-800 eggs in her lifespan. After laying the eggs, the female will die. From these little eggs, a new life cycle will begin.

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The eggs of black soldier fly | Source

Let's check out the life cycle below:

Egg to larvae (4-5 days)

BSF eggs are very tiny & they usually cluster up together. The average weight of 1 egg is around 25 microgram. In 2.9 grams of eggs, you'll have about 99,000 to 116,000 individual eggs.

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Mother fly laying eggs in cardboard gaps | Source

Female soldier flies like to lay eggs in the crevices of wood or cardboard pieces near smelly places with decaying organic matter. Here, the eggs will be protected from other predators, the loss of moisture & be near a food source when the babies first emerge out.

It takes around 4-5 days for these eggs to hatch. After hatching, they will turn into little wiggly hatchlings with cream-like color. They're super tiny & may be a bit difficult to see sometimes. As you can see here are some newly born larvae:

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Newly-hatched baby larvae

Here are the eggs & the egg shells before and after hatching. They turn darker in color, more fluffy & lighter.

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After hatching, they move on to the larvae stage:

Larvae to pupae (15 days)

At this stage, people usually feed the larvae with chicken feed + water, bran, soybean meal, spent barley, rolled oats or any veggie scraps they have lying around. They key is not to overfeed them. It's good to start with something a little bit more fresh first, then we can move on to some hardcore rotting or waste organic materials later. The larvae eat like horses at this point.

The larvae get their water from the food itself. So the moisture content around 60-70% in the food is good for their growth. Too much water in the substrate may drown them. Too dry a substrate makes them shed their skins a bit more, which may affect their health when they grow up according to some raisers.

You'll see the larvae get around 5000x as big compared to when they just hatched. If you leave them hungry for a day, they'll shrink hugely in body size. After devouring food for about an hour, they will boom up so fat.

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Big larvae of black soldier fly

During this eating process, you may see pieces of shed skins around the bin. This is the larvae shedding their exoskeleton (a bit like that of a snake). It's a sign they are growing up. Some people say the more skin they shed the bigger they'll grow. It's good to get the skins out of the pile or just put them in another compost bin.

Also during this process, the larvae will produce some poop or castings. This gets mixed in with the foods & the skins. Filtering these out every 3 days works well to give the larvae a nice, cool environment to grow. People use this larvae castings + left-over foods + exoskeletons for further composting, feeding red wigglers/fish/pets or fertilizing plants.

After about 15 days when they have eaten enough, the larvae will turn a bit more gray, charcoal or dark brown. They will find a suitable dry place to get out from the wet food bedding we provide them. This is when they are ready to turn into the pre-pupae stage.

These darkened larvae are pretty scared of water. They usually leave behind some dark poop in the process of cleansing their guts and discharging undigested food pieces. If you notice this poop around the corners of the box, clean it up as it may affect the other remaining cream larvae that have not turned dark yet.

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Cream larvae turning gray or charcoal | Source

If you feed them white soya bean, you may also see that the food has turned quite blackish. This is the frass or the left-over of larvae food mixed with a bit of the larvae poop. If the substrate is not too wet, you can collect this stuff & use as a fertilizer. The juice works great as a compost tea or to keep houseflies away.

Before turning into pre-pupae, baby larvae will transform its mouth-part into a hook-shape structure. This helps them hook onto surfaces easily on the way out. With this zip-line, it also means they won't develop a mouth as they mature. Also, when one crawls out to find a good spot, it excretes some kind of pheromone. When the other ones catch this smell, they will follow the path out.

Although they may come from the same egg, the larvae may not turn into pre-pupae at the same time. This may be because of the density in the larvae box, the position of the larvae in the crowd, the food or some temperature factors. It's really ideal for some large-scale operations to get a uniform population to get good reproduction & keep the colony rolling.

As the pre-pupae grows up:

Pre-pupae to pupae (14 days)

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Charcoal black soldier fly pre-pupae | Source

When the pre-pupae crawl out to find a dry place, they usually bury themselves under a substrate or material. People usually use sand, sawdust or coco peat this this point. Under this layer is where the magic happens. They undergo metamorphism & all kinds of exciting transformations. The pre-pupae don't eat much at this point.

Some growers worry that if the pre-pupae bury themselves too deep into the ground, how are they able to breathe or survive? Will doing so suffocate them? It's truly magical when people observe the pre-pupae. When these little guys are ready, they'll crawl themselves back up to the ground. At this point, they'll have a pretty hardened shell. And it is also at this point when they stop wiggling. Some think these are dead, but they are not!

Half way or near the end of this process (or approximately on day 26-33), these pre-pupae will stop wiggling & start to elongate themselves. If you scoop some pre-pupae in one hand & let them free-fall down, you'll hear some crumbly cereal-like sound. Their exoskeleton shells or cocoons are a bit more hardened & dry.

If you place a darkened pupae into the water, they will float. We should only do this if we're filtering the pre-pupae out from the frass (remaining undigested foods + poop) by flotation. Otherwise, they prefer a dry place. In contrast, if you put the younger cream-body larvae in water, it will sink or drown.

After about 2 weeks from pre-pupae, these creatures will turn into pupae. The key during this process is dryness & some good shade. Let's see next:

Pupae to adult fly (7-9 days)

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Adult soldier fly spreading its wings | Source

After about 1 week in the pupae stage, the pupae will shed their cocoons & turn into flies. When they turn into flies, they will naturally seek a light source to mate. The adult flies don't eat but only drink. You can collect their shedded skins & re-use them for composting if you like. But the fun doesn't stop there.

Fly to eggs (7 days)

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Black soldier fly depositing eggs | Source

During the first 3-4 days, the flies need to fly around to find a lovemate to mate. During these first few days, they're growing & maturing their sexual organs. We may not see mating in these first days.

When they are sexually mature & find a good partner, they'll go tail to tail. Sometimes, they mate in-flight. On day 5 or 6, the females will lay their eggs. Shortly after that the flies will die.

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Black soldier flies mating

After some days, you can see some white-cream stuff inside the gaps of a wood piece or a piece of cardboard. Those are the deposited eggs. From the eggs then, a new life cycle begins again. It's good not to move or disturb the eggs too much. It may affect their viability.

Usually, when black soldier flies land on a leaf or any materials around, they will stay still. If you see them landing on foods or something but they keep moving left, right & around, you'll know that it's a mother fly looking for a place to lay her eggs.

Also, as the adult BSF lives for only a week or so & they don't have a mouth-part, they won't eat rotting stuff, land on your food or cause any diseases. The adult soldier flies only drink at this stage. So water is good enough for them. Some growers mix sugary water for them.

Other plant some trees with juicy leaves like small papaya trees, freshwater mangroves (Barringtonia acutangula) or chinaberry tree (Melia azedarach). From their experience, when the flies land on these leaves, they'll be able to suck out some of their wax or latex, which keeps them hydrated.

Check out this BSF laying eggs in cardboard close-up:

Total life cycle: 40-50 days

If you've been counting, the total days for black soldier fly going from eggs to adult flies are around 40-50 days or about 1.5 month on average.

The shorter & longer days difference is because of the temperature difference and other environmental or food factors. If there's still food around the space, the baby may stay there for longer to consume it. If there's too little food, they may turn charcoal & pupate sooner.

In the cooler/winter months, the whole life cycle may take up to 5-6 months. In warmer climates, it's a very fast production cycle overall. The majority of the eating happens during the larvae stage. Even with less food, the little larvae won't die off. They are pretty durable & will only shrink in size when there's food shortage. If it gets below 20F (-6C), the larvae may die.

If we take a look at their growing stages, you can see a great size difference.

Growth stage Weight (grams)
1 egg 0.000025
5 days old larvae 0.0012
15 days old larvae 0.125

As you can see, from a tiny egg of 25 microgram it grows 5000x its body to 0.125 gram (15-day-old larvae) in just about 2 weeks. In summary, the cycle goes a bit like this:

  • Egg: from the eggs, about 4 days the hatchlings will hatch
  • Larvae: Tiny cream-body larvae will grow to bigger ones within 2 weeks. They eat ferociously at this stage. Keep the feeding area cool because these wiggling bodies generate quite a lot of heat altogether.
  • Pupae: when the larvae are done eating, they turn a bit black & enter the pre-pupae stage. It lasts for about 2 weeks. Then, the pre-pupae will turn into pupae. After about 1 more week, those pupae will turn into flies–totaling 3 weeks for this whole stage.
  • Fly: the flies only live for 7-8 days. During their short life span, they need to find a mate for reproduction. Adult flies only drink. After mating & laying eggs, the flies will die off.
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When to harvest

Depending on the usage purpose, some people harvest the larvae at that stage to be used as food for their chickens, fish, reptiles, birds or shrimps. Five-day-old larvae are yummy treats for pets. It's easy for baby chicks to chew & contain a good amount of proteins and fats.

If you're using black soldier flies to treat bio-waste or garbage waste, you can put the eggs or hatchlings right on the organic matter for them to digest. They are extremely efficient at converting waste into usable protein & fat sources. Some places shred the waste food to make it easier for the youngsters to eat. About 600,000-800,000 baby larvae will be enough to consume 1 lb of organic waste.

If you're also raising flies as mothers & fathers for reproduction, then set aside about 1% of the larvae population or any numbers you see fit. These guys are usually fed with a special diet that's higher in protein & fats like rotting fish, dead birds, meats so they have good strength to reproduce & not die off easily after pupation.

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