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 begins.
Egg to larvae (4-5 days)
The 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.
In the crevices of a wood or cardboard piece where the mother fly lays eggs, 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.
Larvae to pupae (15 days)
At this stage, people usually feed the larvae with chicken feed + water, bran, soya bean, 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. You'll see them get around 5000x as big when they were just 5 days old. If you leave them hungry for a day, you'll see a huge shrinkage in body size. After devouring food for about an hour, they'll boom up so fat.
After about 15 days when they have eaten enough, the larvae will turn a bit more gray or charcoal. 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 pre-pupae.
If you feed them white soya bean, you may also see that the food has turned quite blackish. This is the compost 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. This is a sign the baby larvae have been enjoying the food.
Before turning into pre-pupae, baby larvae will turn 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. The others smell this & follow the path out.
Pre-pupae to pupae (14 days)
When the pre-pupae crawl out to find a dry place, they usually bury themselves under a substrate or material. Under this layer is where the magic happens. They undergo metamorphism & all the exciting transformations. After about 2 weeks, they will turn into pupae. The key during this process is dryness & some good shade. When they are ready to turn into flies, the pupae will stop wiggling. They just lay there unmoving.
Pupae to adult fly (7-9 days)
When the pupae shed their skins, they will turn into fully established black soldier flies. This happens from 7-9 days after their pupation. 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)
During the first 3-4 days, the flies need to fly around to find a lovemate to mate. When they find a good partner, they'll mate. You'll know when they're mating if two flies go tail to tail. On day 5 or 6, the females will lay their eggs. Shortly after that the flies will die.
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.
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 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. You can try experiment with this if you like.
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 a month & a half 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.
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.
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.