BSFLs in Outdoor Worm Beds

A little while back, RWC reader, Margie (from California), sent me an email sharing her experience with black soldier flies in her outdoor worm bins. I thought others might find the info helpful, so I asked Margie if it was ok to post it here. You can probably guess what she said.
(Thanks again, Margie!)

Below you will find her description, along with images of her outdoor bins

Hi! I have had four large plastic outdoor composting systems for several years. In the beginning, I used to have problems with black soldier flies (BSF’s), which look larger than your average fly and make a crazy and very loud rattling sound when flying. They like to lay eggs and have their larvae grow up in the supportive enviroment of a worm bin (where their larvae will quickly out-eat your wonderful red wigglers).

To deal with this situation, I make sure that my food stuff is “buried” well. After adding the food close to the bottom of the feeding side of the bin, I cover it with approx 5 inches (13 cm) of the more mature compost. Something that has really helped is that I’ve started to add a thick layer of cardboard or shredded paper to the top of my compost. With this technique, I haven’t seen the BSF’s for years now.

Sometimes I even leave the tops of my bins open with a simple large screen on top to promote air flow! Even with this easy access, I still don’t see any BSF’s! The layer of paper is also a great way to prevent fruit flies as well! I’ve never had swarms of them since I started to “buffer” my compost.

One tip for an easy source of shredded paper is to use the leftovers from your confidential paper shredder (if you have one). I know that people say the bleached paper irritates the worms, but if you have a large enough system it really doesn’t seem to bother them at all, especially if you work it into the compost slowly. As you may be able to see in the picture, the bottom layer of the shredded paper absorbs the moisture from the compost and starts to break down quickly. The worms seem to decompose the white paper just as happily as they do cardboard!

The reason I can leave my bin open with a screen on top is that I live in California, and we have a very defined rainy season. Our summer is very dry, with almost no chance of rain. I do get other visitors to my bin though, such as spiders, slugs and earwigs. They’ve never been a problem of excess, and I think of it as a happy habitat and balanced ecosystem.
Hope this helps!
-Margie in California

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  1. A lot of folks would love to have Black Soldier Flies volunteering in their bins. What sort of problems did they cause in your outdoor bins?

    • GA
    • August 7, 2012

    I think her general point is very helpful. To put a slightly different way, adding _lots_ of shredded paper/cardboard (‘bedding’) on top has very few downsides as far as I can tell. Excess water in the main is absorbed, there’s nice loose materials to bury food under, and the extra bedding keeps annoyances (bugs) down and away and lets air flow. Those in wetter climates can cover with a plastic top which will keep some moisture in while keeping excess out (I almost never add water, or at least rarely).

    Only downside for outdoor systems I’ve found is that it’s perfect for mice in winter. Which doesn’t personally bother me that much, but it can occasionally be disturbing to surprise them. I don’t find that the bleached paper disturbs anyone if it’s laid on top and just let to disintegrate into the system on its own. (Not scientific though)

    • The Garbage Guru
    • August 8, 2012

    Kind of odd.But i noticed this year i can’t seem to attract any BSF.Saw one on the hood of my truck.So i know they are in the area.If they ever do get into your bin though,it is almost impossible to get rid of them.I’ve had occasions where i was sifting vc in front of a big shop fan.The BSF get a whiff of the larvae in the air,and show up.Even sitting right on the fan.
    Also if you use horse manure,be prepared to get some BSF as well.Not sure why they like horse manure? But they do.
    I haven’t had any issues composting bleached paper.In fact i have been putting in whole sheets,and the worms congregate between the sheets of paper.

    • Bentley
    • August 8, 2012

    MIKE – True enough, but in lots of cases they can be very frustrating for those wanting to focus primarily on vermicomposting. When conditions are hot and not enough is done to maintain a healthy worm habitat (such as keeping it well stocked with bedding materials), the BSFLs can pretty easily dominate the system.
    GA – Absolutely! Apart from “over-feeding”, I think “under-bedding” (haha) is pretty well the most common reason for encountering issues with a vermicomposting system.
    LARRY – Nice you see you ’round these parts! (wink wink)
    That’s really interesting re: the adults sniffing out the larvae – makes good sense too.
    As for the bleached paper – really, the only caution I have for people is avoiding setting up a brand new system using ONLY bleached paper (that hasn’t been soaked and drained) as the bedding. I’ve added plenty of established systems without any issues.

    • LInda from CA
    • August 10, 2012

    Thanks so much for the info on BSFs. I’ve been so disappointed twice now from them taking over my bin and destroying my red worms. I now know what they are!

    • Wjason777
    • June 8, 2013

    Hello, I just recently build a VB48 and the bsfl population is taking over. Its like the more I feed my worms the more larvae I see. I added a level of shredded paper on top then newspaper on top of that but hat still doesn’t seem to help. Any suggestion on what I should do?

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