Large Flies in Worm Compost Bin

From Bonnie:

I have a recent problem with large (horse?) flies in my worm compost
bin. Fruit flies are not a problem but I do not know how to get rid of
the large flies. There are quite a few. Thanks for any help you can

Hi Bonnie,
My hunch is that those are Black Soldier Flies since Horse Flies wouldn’t likely be attracted to a composting system.
Apart from putting the system inside some sort of screened enclosure, I’m not really sure how you can prevent soldier flies from laying eggs in an outdoor worm bin. Black Soldier Fly larvae are great composters as well, but you may find that they outcompete your worms over time (eating all the wastes and creating an environment that is unfavorable for them).

The ideal outdoor system for allowing them both to coexist would likely be a larger bin in a shaded or partially shaded location, with an open bottom and pit down below so the worms are able to hang out below the bsfl zone where it’s cooler.



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  1. Hi Bentley,

    Cut back on the food and make sure you’ve got plenty of damp cellulose in the bin. BSFL are not particuliarly fond of cellulose. As you know, the worms love it.

    • John
    • June 1, 2012

    Last summer I had a pretty bad BSFL infestation that just about wiped out all my worms. They turn the whole thing to an anaerobic mess. I switched to just coffee grounds and egg carton cardboard. Give the larva some time to drop out and the system will rebound.

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