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.
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.

Location: California

12 Responses to Soldier Fly Larvae in the Compost Bin

  1. wormfarmer says:

    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…?

  2. Bee girl says:

    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!

  3. Simon says:


    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.

  4. Simon says:


    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.

  5. Jason says:

    Im here in Savannah, GA and I have a lot of theses larvae in my compost bin also.

  6. Alicia says:

    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!).

  7. swetha says:

    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

  8. Xaviera Taylor says:

    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.

  9. Paul Logan says:

    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!

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