Are Black Soldier Flies Good For Compost?

In this article, we look at how black soldier fly larvae are the perfect way to compost waste materials.

Be it as a feed supplement or for breaking down yard waste, black soldier flies have earned a name among traditional composting circles.

They help create compost with high nutrition levels, resulting in better plant growth.

With optimum moisture levels, you, too, can convert your agricultural wastes, household food waste, animal waste, and other kitchen scraps into a compost pile.

Let’s dig into how these flies can help turn your kitchen waste into something better.

Probably Black Soldier Fly

What Are Black Soldier Flies?

Black soldier flies, or Hermetia illucens, are a type of commonly found fly belonging to the Stratiomyidae family.

They closely mimic the organ pipe mud dauber wasp, even having a thinner abdomen, giving them the famous “wasp waist.”

Since the 20th century, soldier fly larvae have become increasingly popular as compost-friendly insects that help break down matter.

They are even shipped in the larval stage to various agricultural farms that want to produce compost.

The main difference perceivable to the naked eye between a common housefly or blowfly larvae and black soldier fly larvae is that the latter has a gray-black stripe on its rear.

What Nutritional Benefit Do They Add To Compost?

Black soldier fly larvae are great sources of protein. Their bodies contain around 50% crude protein and 35% lipids.

Along with this, they are a good source of amino acids.

BSFL (black soldier fly larvae) bodies contain some beneficial amino acids, such as lysine and threonine.

These cannot be obtained from plants, making them a good addition to animal and chicken feed.

They are also consumed by humans in some parts of the world. As long as the flies are blanched, they’re safe to consume.

Many insect factories run by biotechnology companies produce black soldier fly larvae, which are then shipped to various farms.

When compost made with BSFL frass was used, it resulted in better vegetable yields.

Black Soldier Fly Larvae

The BSF frass fertilizer also had more nitrogen, calcium, phosphorus, and potassium than homemade compost without BSFL.

However, the benefits of BSFL also come from what the larvae feed on. The best larvae are those that feed on organic matter that has rich, digestible nutrition.

Larvae exposed to toxic chemicals, heavy metals, and pesticides carry them forward and can introduce the substances into compost and animal feed if added.

How is Black Soldier Fly Composting Different From Normal Composting?

There are minor stage differences between composting with BSFL and normal composting:

Firstly, BSFL are more adept at quickly digesting different types of organic materials that take time with traditional composting methods.

You should monitor the amount broken down in a day and add the same quantity, decreasing it toward the end as the larvae grow older.

Soldier fly larvae need a varied diet. Usually, traditional composts are made with equal parts nitrogen and carbon, classified as brown and green organic matter, respectively.

BSFL, on the other hand, requires more animal products and processed products.

This makes it ideal for home composts, as cereals, coffee grounds, and waste meat can all be added to the pile.

How To Compost With Black Soldier Flies?

Composting with BSFL essentially means adding them to the substrate so that they can help with the composting process. After this, you can harvest the larvae and add them to poultry feed.

It’s important to note that it’s the larvae that help with composting and breaking down organic matter. Adult flies do not feed.

Hence, you should harvest the larvae while they’re in the pupal stage – at the latest—or you’ll end up with a lot of pesky flies!

Here are the steps to creating compost with black soldier fly larvae:

  1. First, you need to rear the larvae. You can do this in a specific rearing bin that has some substrate or directly add them to the compost. The substrate can be slightly damp coconut coir, straw, shavings, and coffee grounds.
  2. Offer the larvae different types of food items. Variety helps with quicker development. Ideally, 10,000 larvae feed on around 4 pounds of food items a day. This can be rice, vegetables, or fruits. Ensure that the earlier added food is broken down before adding more.
  3. During this stage, you need to keep your bin within a relative humidity of 50-70%. It’s best to use a sealed bin with a monitor. A good humidity range is essential for the larvae to get to work.

Once done, sift the larvae out. You can now use the composted matter as soil manure or livestock feed.

Are Black Soldier Flies Good For Compost
Black Soldier Fly Larvae

To turn the larvae into feed, blanch and dry them, and finally pulverize them.

Alternatively, you can keep the larvae in the bin and repeat the composting cycle, or simply place them elsewhere in your garden.

Larvae do not feed on live plants. As flies, they might return to the compost pile to lay eggs again.

It’s always advisable to test BSF compost before adding it to plants. Sometimes, it might contain digestive toxins or high levels of salt, which can negatively affect your plants.

Wrap Up

Black soldier flies aren’t pests. Since adults don’t feed (or bite), chances of them transferring any bacteria onto a human are rare.

If you do find them around, try investing in a small compost pile. These insects have high and efficient food conversion rates.

The final frass produced is odorless, making it ideal for smaller homes.

If you do smell the odor, it means the earlier food given has not yet been converted and has instead decomposed by itself, prompting bacterial growth.

Thank you for reading.

Frequently Asked Questions

How does black soldier fly compost work?

Composting with black soldier fly larvae (BSFL) involves adding them to the substrate to aid in the composting process.
Only the larvae help with composting, not the adult flies. Harvest the larvae while in the pupal stage to avoid an infestation of flies.
Rear the larvae in a specific bin with the substrate or add them directly to the compost. Offer them a variety of food items and maintain a humidity range of 50-70%.
Sift out the larvae and use the composted matter as soil manure or livestock feed. To turn the larvae into feed, blanch, dry, and pulverize them.
Test the BSF compost before adding it to plants to avoid potential negative effects.

How do you get rid of black soldier fly larvae in compost?

To prevent or control fly larvae in your compost bucket, empty it weekly, freeze or refrigerate food scraps, snap the lid on and limit openings, avoid leaving food out, and spray them with vinegar.
Keeping the bucket outside can also limit exposure to larvae. BSF eggs take 4 days to hatch, so weekly emptying is important.
Boiling water can kill larvae, but vinegar can also be effective. Testing with different types of vinegar is ongoing.

What are black soldier flies good for?

Black soldier flies are a good source of energy and clean food as they eat a lot and their digestive processes kill bacteria.
They reproduce at a higher rate than cows and are easy to farm and harvest. They are efficient at converting feed into food and have a short life span of only 6 weeks.

Do black soldier flies eat manure?

Black soldier flies (BSF) have been known for over 100 years and were initially considered pests that should be exterminated due to their presence in smelly farms and latrines.
However, early scientific papers discovered that BSF eats manure and has economic value.

Reader Emails

There is a lot of interest in black soldier fly composting, and the proof of that is in the number of reader queries we got regarding this topic over the last few years.

Go through some of the emails and our replies below.

Letter 1 – Soldier Fly Larvae in the Compost Bin

 

weird bug/larva in vermicompost July 27, 2009 I’m thrilled to be new mom to a worm factory since the original owners are moving out of state. I just found some weird bugs that I thought may be a type of beetle larva, but I really have no idea. If they won’t harm my worms, I’ll put them back in the composter. They seem to be segmented, dark gray-brown, no legs or discernable head but do travel in one direction from the pointy part (that looks like the tip of a fine ballpoint pen) by moving the little hairs that cover them. There are more hairs on the bottomside. They’re pretty big, about an inch long and quarter of an inch wide. Kind of creepy. but I love bugs and would love to know what the heck they are. Thanks for your help. wormfarmer vermicompost bin in pasadena, ca
Soldier Fly Larvae
Soldier Fly Larvae
Dear Wormfarmer, You have Soldier Fly Larvae, Hermetia illucens, a species Charles Hogue refers to as a Window Fly in his book Insects of the Los Angeles Basin.  The following is an excerpt from the Oregon State University Garden Hints website and the quotes are from Cindy Wise, compost specialist volunteer coordinator with the Lane County office of the Oregon State University Extension Service.  “Soldier fly larvae are voracious consumers of nitrogen-dominant decaying materials, such as kitchen food scraps and manures. ‘Don’t worry, soldier flies don’t usually invade houses, unless your compost pile is close to your house,’ said Wise. ‘They almost exclusively populate compost bins or sheet mulch compost piles and manure piles,’ she said. ‘In the southern United States they are being utilized to reduce hog manure, as they can consume up to 30 tons of hog manure in two days.’ Soldier fly females lay eggs on the surface of nitrogen-rich material that is exposed. So, if you want to avoid having these large flies and their maggots in your compost pile, make sure you have enough leaves, dry grass, shredded paper and other organic “brown” material in the pile to cover the nitrogen food sources by at least two to four inches. Be sure to bury food scraps deeply in the pile and cover them well. You can further discourage these flies by putting window screen over any holes in the bin and gluing it down with a waterproof caulking (like an exterior household caulk) on the inside of the bin to help exclude the flies in their egg laying stage. They often thrive in worm bins, as well as compost bins, where they may out-compete the worms for food. ‘In a worm bin, bury food scraps down at least six inches for the worms and let the flies eat what is on the surface,” said Wise. “The flies don’t eat the worms or their eggs so they aren’t predators of the worms.’ … Wise and her colleagues are experimenting with soldier flies in compost bins and then analyzing the resulting compost to see what differences there may be in the nutritional content of the compost. The maggots are known to break down organic material in the pile so it can further decompose. And the flies inoculate the compost with beneficial bacteria from other sources.”  In our opinion, you should return the Soldier Fly Larvae to the worm bin.

Letter 2 – Jumping Spider eats Soldier Fly

 

Jumping spider with black soldier fly Location: Tennessee, suburb east of Nashville August 13, 2011 9:03 am Hello! I recently used your site to identify the large harmless insects and their grubs that we’ve been seeing in the house the last few years (ever since I unsuccessfully tried to start composting) as Black Soldier Flies (who, of course, think the compost box is quite nice!) I thought you might enjoy this picture I took last summer of a jumping spider carrying a Black Soldier Fly. If a spider could look proud, then this one certainly would… Signature: Andrea
Jumping Spider eats Soldier Fly
Hi Andrea, Thanks for sending us your photo of a Jumping Spider eating a Black Soldier Fly.  You have got to be our last identification this morning, and if we post anything else in the next few hours, we are obviously procrastinating something else that we need to get done.

Letter 3 – Black Soldier Fly Lavae in Compost Bin

 

Subject: mystery bug Location: arizona March 2, 2014 8:32 pm found these on a compost bin after a lot of rain in arizona Signature: jas
Black Soldier Fly Larvae
Black Soldier Fly Larvae
Dear Jas, These are Black Soldier Fly Larvae, Hermetia illucens, and they are beneficial in the compost bin as they help break down organic matter.  The rains probably caused the larvae which were living comfortably in the bin to evacuate.  You can try the Black Soldier Fly blog for additional information.
Black Soldier Fly Larvae
Black Soldier Fly Larvae

Letter 4 – Gorgeous Soldier Fly: Hedriodiscus varipes

 

Subject: Soldier Fly–Hedriodiscus Varipes Location: Wilderness State Park, Michigan July 5, 2014 7:25 pm Hello! Sorry I’ve missed a couple of days; I’ve been busy doing research. I’m sure y’all are busy as well! Today, I’ve brought you a soldier fly which I think I’ve got pinned down as Hedriodiscus varipes. The pattern on the head is pretty distinct for this species compared to other Hedriodiscuses–but what really confirms it for me is that Bugguide only has one picture of this species, taken back in 2007, in Wilderness State Park in Michigan… which is exactly where I found my specimen. (Bugguide does note that the species are hard to distinguish, but the genus is right, anyway.) It was very interested in these flowers, avidly dabbing at them with its tongue. This is a very large fly–the size of a horse fly, easily. Signature: Helen
Soldier Fly:  Hedriodiscus varipes
Soldier Fly: Hedriodiscus varipes
Dear Helen, This fly is positively gorgeous, both in color and in markings, and we are quite certain its impressive size added to its beauty.  According to BugGuide:  “Larvae are aquatic” so they are most likely always found near a habitable water source.
Soldier Fly:  Hedriodiscus varipes
Soldier Fly: Hedriodiscus varipes

Letter 5 – Soldier Fly

 

Subject: Green and black horsefly looking bug Location: Lake Charles, Louisiana August 10, 2014 11:48 am I live in Southwest Louisiana and was tending to one of my flower beds today on August 10, 2014 and ran across this bug grooming itself on a coneflower leaf. Could you please identify it for me? I was not sure if it is some sort of horsefly, wasp, or something totally different. Signature: Lyndsey D.
Soldier Fly
Soldier Fly
Dear Lyndsey, This is a Soldier Fly, possibly Odontomyia cincta based on images posted to BugGuide. Thank you so much for identifying this intriguing fly so quickly. I had trouble finding any images at all until you identified it. Sincerely, Lyndsey

Letter 6 – Black Soldier Fly Larvae in Composter

 

Subject: flattened out legless pill bug thing Location: north texas October 23, 2014 8:28 am My parents have this device that makes compost from old bits of banana peels and whatnot, and every once in a while it will leak, so we put this metal tub underneath it. Now the tub has these strange bugs that move like caterpillars, or slugs, and have a back similar to a flattened out “pill bug”. We do not want the bugs in our garage, but are not sure what to do with them, because we don’t want to simply kill them. Signature: nathan
Black Soldier Fly Larvae
Black Soldier Fly Larvae
Dear Nathan, These are Black Soldier Fly Larvae, and they are commonly found in compost piles where they contribute to the decomposition of organic materials.  They will not negatively affect the compost or your family.  They are benign and they should be left to do the job that they do so well.
Black Soldier Fly Larvae
Black Soldier Fly Larvae

Letter 7 – Black Soldier Fly Larvae found near compost pile

 

Subject:  What can be this “larva”? Geographic location of the bug:  Madrid city, NE Date: 03/28/2021 Time: 01:59 PM EDT Your letter to the bugman:  There are lots of this larva (I think that it is a larva, but not sure, perhaps a chrysalis) at my parents flat roof. Many of them near to an open box with compost. Some of them looks alive, some of them are “emtpy”. It is the first time that something like that appears there. Thank you. How you want your letter signed:  Chris
Black Soldier Fly Larvae
Dear Chris, These are Black Soldier Fly larvae and they are often found in compost piles.  They are harmless and are actually considered beneficial as they help to break down the organic materials in the compost pile.

Authors

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  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com 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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12 thoughts on “Are Black Soldier Flies Good For Compost?”

  1. Thank you so much for your prompt and thorough reply. I will let them live in the composter, but you wouldn’t be opposed to a few being given to our chickens, would you…?

    Reply
  2. I live in Queensland, Australia, and have had “window-waisted flies” in my worm farm for a long time – I find that the larvae help to make compost much faster! The flies don’t even seem to need to leave the boxes – it seems that they complete their whole life cycle inside (in the dark) over and over…they also don’t seem to bother the worms much. I find it all fun to watch and lovely to have harmless creepy crawlies to show and teach the kids!

    Reply
  3. Hi!

    I’ve got the same larvae in my compost pile, here in Portugal.
    In summer there are so many beneath a slice of bread, that I can catch a handful of them. It appears that the fly is worldwide.

    Reply
  4. Hi!

    I’ve got the same larvae in my compost pile, here in Portugal.
    In summer there are so many beneath a slice of bread, that I can catch a handful of them. It appears that the fly is worldwide.

    Reply
  5. We have discovered an exodus of these interesting larvae moving from our patio towards the dirt backyard over the last 24 hours. We’ve had a great deal of rain here in Tucson, AZ over the past two days and it appears to have brought them out in droves. We will toss them into the compost bin, and perhaps give a few to the neighbors’ chickens (who will be most appreciative!).

    Reply
  6. I have been seriously composting since a year and was discouraged by finding these worms in my bin, I didn’t wanted to quit so was trying my own ways, but finally by visiting Your site I’m so happy and relieved…Thanks a ton

    Reply
  7. I had a ton on my compost bin following a couple of rainy days. Thanks for the great info. I’m homesteading in NC by the way. We haven’t found any in the earthworm bins as of yet.

    Reply
  8. I’m new to vermicomposting and all was going great. A few rainy days and me not checking on the compost bin ended in what seems like a ton of the solider fly larvae. I started hand picking the worms out the bin n putting them into a larger vermicompost bin b4 I read this thread. I’m so relieved that it’s nothing harmful cause I’m raising cocoons in the bin and was afraid they would be in danger or get eaten. You just saved me a few days of picking thru the compost bin. Thank you very much for explaining exactly what they are and where they came from. Thank you!

    Reply

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