Small black beetles in my worm bin
Tiny, oval black beetles in a worm bin are most likely feather-wing beetles. They eat decaying matter and fungi and don’t harm worms. Rove and ground beetles can eat small creatures, but they’re usually too few to matter. If your worm numbers stay steady, ignore them and simply don’t overfeed.
Hi, I’ve kept red wigglers for many years and from time to time I get little black beetles in my worm bins. As most beetles are carnivores, I was wondering how destructive they can be, and whether you know what they are? I haven’t seen a major drop in my worm population but just want to be sure!
Hello,
Apart from worms, worm bins can host quite a lot of small creatures, including different kinds of beetles. Without a photo and more information it’s very difficult to identify a beetle clearly.
The beetles most often found in worm farms are rove beetles and especially feather-wing beetles. Feather-wing beetles can be found in considerable numbers, but they only feed on decaying matter and are no danger to worms.
Rove beetles and ground beetles can be predatory and feed on small insects, slugs and worms, but they usually occur in such small numbers inside worm bins that they don’t really affect the worm population.
I usually ignore beetles in my worm bins and have never had a bad experience with them.
Later in the thread the reader, an entomologist, confirmed they were not rove beetles but very tiny oval beetles, and Stephan suggested looking at feather-wing beetles, which he often has in his own bins without any problems.
The full answer
Worm bins attract all sorts of small creatures. After nearly 30 years of worm farming, first in South Africa and then in Germany, I still find new ones. Here’s how to tell whether your beetles need any action.
What are the tiny black beetles in my worm bin?
The tiny oval ones, often less than 1 mm long, are most likely feather-wing beetles (family Ptiliidae). They are among the smallest beetles in the world and feed on fungi and decaying matter. Other small beetles you may see are rove beetles (long, slim, with short wing covers that leave the tail end bare) and the odd ground beetle (larger, shiny, fast-running).
Are they harmful to my worms?
Feather-wing beetles: no. They eat the same decaying material and fungi as many other helpers in the bin. Rove and ground beetles can eat small insects and occasionally worms, but in a worm bin they’re normally too few to matter. As the reader said, if your worm numbers stay steady, the beetles aren’t a problem.
How do I keep beetle numbers down?
- Don’t overfeed. Leftover, mouldy food feeds the fungi that small beetles live on.
- Bury the food under the bedding and keep the surface covered with damp newspaper or cardboard.
- Check the moisture. Like a wrung-out sponge: not soggy, not dry.
- Remove large beetles by hand if you see rove or ground beetles and want to be safe.
I don’t use any sprays or poison: anything that kills beetles can harm worms too.
How can I identify them?
Take a close-up photo with your phone’s macro mode or through a magnifying glass, next to a ruler for scale. Note the shape (oval or long), the length, and whether the wing covers reach the tail. Send it to me via the free helpline.
What else lives in a worm bin?
A healthy bin is a small ecosystem: springtails, mites, pot worms, fruit flies and beetles all come and go. Most are harmless helpers. For the ones that need action, see maggots in a worm farm, fruit flies, ants and cockroaches.
Still stuck? Describe your bin on the free helpline and I’ll take a look.
Happy worming!
Stephan Kloppert
Nearly 30 years of worm farming in South Africa and Germany
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