Help! Are these maggots in my compost?


A soldier fly larvae


Sam emailed in a photo of some brown grubs he said have been populating his compost bin, concerned they might be doing it more harm than good.

But good news Sam, these little brown larvae are one of the good guys!

They are the larvae of Hermetia illucens,  or more commonly called black soldier fly. 



Black soldier fly larvae (BSFL) are actually beneficial to your compost heap or bin because:

  • they’ll help prevent houseflies from laying their eggs in your compost.
  • they actually help in the breakdown of your compost

So don’t panic if you see these little brown grubs in your compost bin – they are giving you a helping hand!

An adult black soldier fly

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2 Responses

  1. Jeff

    I recently set up a red wriggler worm colony about one month ago with 1,000 worms. I left them alone knowing they like darkness and dampness, and this morning I thought I would see how they were doing.

    There were only 4 Red Wrigglers left! But there were about 50 BSF Larva, which I didn’t know what they were at the time and was thoroughly disgusted- thinking, these maggots ate my worms!

    But now I see they are helpful, I think I’ll just put everything into my compost bin instead of a separate worm composter and keep it dark and moist.

    I still don’t know what happened to my worms! I live in Southern CA, any thoughts?

  2. Donald Ross

    Thank you for identifying my yearly infestation of compost maggots. They appear every year and have a great feast on kitchen scraps. I have a pretty tightly closed bin and never have seen a plack fly. Incitentally there is a constant huge colony of cockroaches and healthy worms in my composting menagery which admittedly is a bit wet and somewhat anaerobic but the compost retrieved from the bottom is just fine.


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