The soldier fly marches on

May 7, 2022

The first time I saw soldier fly larvae in my worm bin I did not know what they were other than maggots.  I picked them out with a long tweezer and dropped them on the ground.  My intention was to kill them when I was done.  However, when I looked between my feet, a blue-belly lizard was down there eating them.  Since then, I have learned that soldier flies are considered delicious by chickens, lizards, fish and other creatures.

One time I collected the larvae and put them in a bottle to see what would hatch. Out came a creature looking much like a black wasp.  By then I knew that these insects were great composters. I had been away for two weeks, and when I returned and checked my compost bins, the bin with the soldier fly larvae was down a foot or more. At that point, I knew these were good guys.

Later I read that researchers at an East Coast university were testing the larvae's ability to compost cow manure. On another occasion I saw them returning to a worm bin to lay their eggs.  

Over the years I have had some interesting creatures live in my compost bins alongside my worms. I've seen a couple of small snakes, small toads of all kinds (I thought they were catching fruit flies) and lizards, to name a few. When I learned that soldier flies were high in protein, I wondered if that's why all those other critters were in my bins. They were eating these precious composters. 

I didn't initially suspect that. I thought the snakes were after the tiny toads. I found a snake one day with a toad in its mouth and removed it. The toad loved that; the snake was not so happy. 

Recently I heard about Hermetia Protein, a company in Sonoma County that gathers restaurant waste daily and composts it with soldier flies. This aroused my curiosity and led me to do some research.  I have not seen soldier flies in my bins for a few years and wondered why.   

Soldier flies are native to the Western Hemisphere. The fly itself lives about a week.  It does not sting or eat any food during this time but it does drink water. The larval stage is usually quite long and is the main life of this insect. It goes through six stages as a larva. They are voracious eaters: a thousand larvae eat over two pounds of food a day. They will eat almost any kitchen garbage except eggshells (which worms love), weeds, paper and cardboard.  

If you decide to try soldier flies in your compost bins, don't let their numbers get too big and crowd out the worms, sow bugs and other creatures.  They like warmer weather but the pupae will survive in cool weather.  While they don't like a wet bin, they do like it damp. So you may need to add water from time to time. Make sure your container has drainage holes. 

You can buy soldier flies online.  Some are sold dried, for people who own pet lizards, toads, goldfish and chickens.  Others are sold live so you can raise more for your pets or put them in your compost bin. There are bins made for raising them and YouTube videos on how to set up a bin. On KQED's YouTube channel, you can watch a video about a farm raising the larvae for resale.  They have a special breeding room and play music for them.  Then they collect the tiny eggs.  Each female lays around 500. 

Universities around the country are studying these creatures for various purposes, including recycling, and there are projects to raise soldier flies worldwide. 


Food Growing Forum: Join Napa County Master Gardeners for a forum on growing squash and what else to do in the May edible garden on Sunday, May 8, from 3 pm to 4 pm, via Zoom. Register to receive the Zoom link:

Guided Tree Walk: Join Napa County Master Gardeners for a free guided tree walk in Napa's Fuller Park on Tuesday, May 10, from 10 am to noon. Meet at the corner of Jefferson and Oak Streets. Space is limited to 12 and registration is required at

Composting Workshop: Napa County Master Gardeners will host a workshop on “Home Composting: Worm & Rapid/Hot”  on Saturday, May 21, from 10 am to 11:30 am, at Napa Valley College Upper Valley Campus, 1088 College Avenue, St. Helena. Learn about rapid (hot) composting and worm composting, why to do it and how to build a pile or bin. If you complete the workshop, you can purchase a backyard compost bin for $20 or to get a worm bin kit. Register here. 

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