Black Soldier Fly Pupa

folder_openDiptera, Insecta
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In this article, we will talk about the pupal stage of the black soldier flies, specifically how long it takes, and what factors control its weight and size.

You might be familiar with the tiny, wasp-shaped flies that flit in and around decaying matter and garbage cans.

While they can be annoying, this insect species has a highly efficient rate of converting waste into nutrient-rich compost – are a highly beneficial agricultural ally.

Emerging from an egg to feed on organic matter, to turning into a pupa, to becoming an adult – black soldier flies are more than good composting insects.

They also form good fodder for livestock and their pulverized remains can be used as fish or bird feed.

Let’s take a look at how these larvae go through the various stages of life.

Black Soldier Fly Pupa
Black Soldier Fly Larvae

What Are Black Soldiers Fly?

The Hermetia illucens, also known as the Black Soldier Fly is a black, shiny, wasp-shaped fly commonly found across the world.

They’re mostly found surrounding decaying organic matter, and the black soldier flies larva is responsible for the decomposition and breakdown.

Adult BSFs have a shiny, metallic appearance and can have a range of colors such as blue, yellow, green, or black.

Their body has 3 segments and mimics the look of a wasp with its thin waist. However, they do not possess a stinger.

One way to distinguish an adult soldier fly is to look for the base of their legs, which are white in color.

These flies (rather, their larvae) have been rapidly gaining attention recently as a natural way to break down organic matter and produce high-quality compost for plants and animal feed substrate.

Adult flies live short lives and don’t eat, however, the larvae have a voracious appetite and are the ones that help with the matter breakdown.

Life Cycle of the Black Soldier Fly

BSFs have a complete four-stage life cycle, like many other insects.

Mature flies emerging from a pupal stage start mating within just two days.

In fact, adult flies do not have any other purpose other than mating.

To this extent, they do not even eat food – though they might help with pollination as they move from plant to plant.

Males select potential lekking sites and protect these from other males, waiting for females to drop by.

They intercept female flies entering the area and mate mid-air. After mating, the female lays around 500 cream-white eggs at a favorable place.

This usually means within the nooks and crannies of decaying organic substrates.

The eggs hatch in 4 days. The larvae are segmented, flat-oval shaped, and have chewing mouthparts on one end.

Black Soldier Fly Larvae

They’re only 15 to 20mm long and mimic the larvae of blowflies in many ways.

The larvae will start feeding instantly on decaying matter and go through six instars before forming a pupa around itself.

This process takes around 14 days – hence compost pits with BSFL (black soldier fly larvae) should be emptied bi-weekly to avoid flies.

To form a pupa, the larvae move on to a dry, sheltered area. The pupa is dark brown in color and pupation requires around 2 weeks.

After this, an adult emerges. Adults don’t eat and rely on the fat stored in their bodies during larval development.

However, by providing them with sugary water, adult flies can live longer.

What Is the Pupal Stage of BSF?

After the fifth instar molt, the BSFL enters into a pupa-like stage.

They do not produce any silk or pupal material.

Instead, the outer exoskeleton of the larva darkens into a brownish (or charcoal gray) color, while the insides slowly turn into a fly.

The mouthpart transforms into a hook-like structure for clinging onto the support. Usually, it takes around six hours for the pupa to form, followed by the transformation of the appendages.

How Long Do Black Soldier Flies Pupate?

On average, BSFLs require around 2 weeks of time to transform into a pupa and then emerge as an adult fly.

However, the time varies based on favorable conditions.

Generally, forming the hardened exoskeleton takes 6 hours, followed by 9-21 hours for the mouth to transform into a hook.

At 21 hours, the pupa is complete and the insect is in a pharate stage. Sometimes, adults emerge as quickly as within 8 days.

How Much Do BSF Pupae Weigh?

A single larva usually weighs around 200 mg at the last pre-pupal stage.

As a pupa, their weights may increase or decrease based on factors like the environment’s pH and feeding style (batch feeding vs. daily feeding).

In a study regarding the same, larvae that were subjected to a higher pH transformed into heavier pupa, whereas those in lower pH environments transformed into a lighter pupa.

How Long Does It Take for a Black Soldier Fly Pupa to Hatch?

The BSFL turns into a pupa over the course of 21 hours. Beyond this, it may take up to 14 days for the pupa to hatch into a fully mature adult fly.

After emerging, male flies look for optimal lekking sites.

If a male enters the lekking site of another male, the two engage in a fight, with the winner obtaining the site.

Black Soldier Fly Larvae

How Do You Get Rid of Black Soldier Fly Pupa?

There are many ways to eliminate soldier flies. However, the most efficient way is to simply remove the source of breeding.

This would include the removal of any organic matter piled in and around your home. Use cans with lids for collecting organic waste.

Apart from this, you can:

  1. Simply pick and throw away BSFL and pupa since they are harmless and do not bite. You can move them to another site or boil and pulverize them to finally add them to poultry feed (or as compost).
  2. For adult flies, use a fly swatter.
  3. To prevent eggs, spray a vinegar mix.

Wrap Up

Black soldier fly larvae are fit for human consumption (after treatment) and are a good source of protein.

However, they’re mostly used for chicken manure, fish, and poultry feed. They’re also a great investment for people looking to turn their kitchen waste into compost.

However, if you’re rearing them at home, it’s good to eliminate them at the pupal stage by pulverizing them into larvae feed.

Thank you for reading.

Frequently Asked Questions

How long do black soldier flies pupate?

Black Soldier Flies take around 2 weeks to transform into pupae and emerge as adults, but the time varies based on conditions. 
The formation of the exoskeleton takes 6 hours, followed by 9-21 hours for the mouth to transform. 
At 21 hours, the pupa is complete, and the insect is in a pharate stage. Adults can emerge as quickly as within 8 days.

How fast does black soldier fly grow?

Black soldier flies (BSFs) have a four-stage life cycle, and adult flies only mate and do not eat food. Males protect potential mating sites and intercept females to mate mid-air.
Females lay around 500 eggs in decaying organic substrates, which hatch in four days. 
The larvae feed on decaying matter and go through six instars before forming a pupa in a dry, sheltered area.
Pupation takes around two weeks before an adult emerges. Adult flies rely on the fat stored in their bodies during larval development but can live longer with sugar water.
Compost pits with BSFL should be emptied every two weeks to avoid flies.

How many eggs does BSF lay?

The female black soldier flies around 500 eggs in decaying matter like dung, carrion, and organic waste. The eggs hatch into larvae in four days.

What are the disadvantages of black soldier fly larvae?

Black soldier fly larvae are a popular solution for organic waste management, but there are concerns about their effectiveness.
They are usually fed consumer-level organic waste, which includes byproducts that can be recycled as human food products.
This means they are not reducing food waste as a whole. Food waste is a significant global issue, with around 13.8-15.3% of food produced going to waste before it reaches consumers. This causes a significant amount of greenhouse gas emissions.
While black soldier fly larvae are experts at consuming almost anything, the efficiency with which organic material is converted into insect biomass depends on the type of feed given to them.
Farmers may face a financial burden to find a reliable and budget-friendly feed source for the flies.
The best black soldier fly diet highlights the suitability of biodegradable waste, making it a significant contributor to environmental damage.

Reader Emails

With the growing interest in ecologically sustainable insect farming for composting, there are a lot of questions that our readers pose to us about black soldier flies.

While we haven’t been able to cover everything about the crucial pupal stage of these flies, some of these questions and their answers are enumerated below. 

Please go through some of them below, as they might give you the specific answer that you are looking for.

Letter 1 – Black Soldier Fly Pupa


What is this? February 16, 2010 We live in an apartment in Los Angeles, CA. It is February 16th 2010, This is one of third of the same bug we have found in our apartment. All of them located around 2-10 feet of the living room closet. We found them on the ground. We have hardwood laminate. They are slow crawlers, and act dead when touched. Could you please tell me what this is and where they are coming from? Thank you, Martin A Los Angeles, CA
Black Soldier Fly Pupa
Hi Martin, This looks like the pupa of a Black Soldier Fly or Window Fly, Hermetia illucens.  We get numerous reports of countless Black Soldier Fly larvae in compost piles.  If there is a nearby compost pile, the larvae may be migrating to your apartment.  The Black Soldier Flies are neither dangerous nor pests, and according to BugGuide:  “larvae compete with house flies in manure, compost piles, etc., and may thus be beneficial. Adults are harmless and not known to carry any human disease.”  The Black Soldier Fly Blog has some good photos, and there is an entertaining video on You Tube of an adult emerging from the pupa.
Black Soldier Fly Pupa

Letter 2 – Black Soldier Fly Pupa


larval stage of what bug? Location: Temecula, CA August 23, 2011 9:19 am This morning I found many of these dead under a hanging petunia basket, many dead in the family pool, and one crawling and almost ready to drop in the pool. They’re all about 3/4 inch long. I don’t know if they dropped from the basket because I had sprayed ant insecticide onto the slab(boy, we have been overrun with ants!)so they may have wandered into the dead zone from somewhere else. They crawl like maggots but these don’t look like the housefly white larva. Signature: Gene
Black Soldier Fly Pupa
Hi Gene, We have categorized this as a Maggot on our website.  It is a Black Soldier Fly Pupa.  The Larvae of the Black Soldier Fly are very common in healthy compost piles, and they often wander away from the compost when it is time to pupate.

Letter 3 – Black Soldier Fly Pupa


Subject: Is this Botfly larvae Location: South padre island April 2, 2017 4:40 pm Please help identify Signature: Vivian
Black Soldier Fly Pupa
Dear Vivian, This is definitely an immature phase of a Fly in the order Diptera, and we do not believe it is a Bot Fly.  We needed to research that South Padre Island is in Texas.  We suspect this might be a Black Soldier Fly pupa.  Was it found near a compost pile? 

Letter 4 – Black Soldier Fly Pupa


Subject:  What’s this bug/worm in standing water? Geographic location of the bug:  Northern CA – Mendocino Coast Date: 11/11/2017 Time: 04:59 PM EDT I’ve been seeing a lot of these worm bugs floating/swimming in the standing water on top of my composter.  They are alive and move around slowly in the water.  They’re almost an inch long and kind of skinny if you see them sideways (2nd photo).  Can you tell me what this is? Thanks so much! How you want your letter signed:  Laurie York
Black Soldier Fly Pupa
Dear Laurie, This is a Black Soldier Fly Pupa, and their presence in your compost pile is a sign that it is healthy.  According to Daily Dump:  “The Black Soldier Fly Maggots are prolific creatures that appear in all compost heaps – they are nature’s scavengers and good for composting. They love a very wet pile. …  If it’s too much and you want to avoid them coming out and crawling on your floor, you can put your composter in a plastic tub with high sides. They usually cannot crawl out of that slippery vertical surface. If they crawl out and wander all over, then sweep them up, collect them in a container and drop them under a tree – birds love them!  Remember that these BSF maggots suppress the lifecycle of the pest carrying housefly. The Soldier flies have no mouth and cannot transmit pathogens, so they are harmless. Appreciate them. They are even a fried delicacy in some cultures as they are very rich in protein!” 
Black Soldier Fly Pupa
Hi Daniel, Thanks so much for writing me with this info about the Black Soldier Fly Pupa.  Now when I see them I’ll not be frightened and know that they are beneficial in my compost pile. I appreciate the helpful info you sent me. Be well, Laurie


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Black Soldier Flies

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9 Comments. Leave new

  • BSF in da House!! [not intended as a cruel joke on the writer of this letter]

    the larvae and pupae of BSF are definitely edible, though granted most people might not consider them the prettiest food around. They can be reared in huge amounts from non-stenchy food sources, rinsed easily, and ground into flour.

    I know of a primitive skills living community in NC that sorts these bugs out of their compost and consumes them. Haven’t tried it myself. Yet.


  • why and how are these pupa things getting in a toilet ? do the swim up in the water in the toilet? could they live in your plunger in the bathroom if the fly laid eggs there?
    thanks, just a little freaked out.

  • why and how are these pupa things getting in a toilet ? do the swim up in the water in the toilet? could they live in your plunger in the bathroom if the fly laid eggs there?
    thanks, just a little freaked out.

  • Chrischan Stephens
    May 29, 2017 12:03 pm

    I recently purchased an RV, and about a week/2 later I have these crazy Lil critters. I have put the RV on a permanent septic system(no longer using the holding tanks solely). Could they be coming from there? And what is a good deterrent?

    • Did you ever figure out where they’re coming from? Because they are just now appearing up in my camper as well.

    • I came home to my RV yesterday to these all in my toilet. What do I use to rid the RV toilet from these? they are freaking me out!

  • I found TONS of these squirming around in the mulch and dirt bottom of my parakeet aviary. SO GROSS!!! I can’t treat because the insecticide will affect my parakeets! Ugh.

  • A friend of mine is an ichthyologist who is trying to farm sturgeon in order to produce caviar. He uses soldier fly larvae as fish food.


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