I have never heard of gnats in a worm bin. Of course there is a first time for everything. I suspect you are talking about some sort of tiny flying insect that wanders away from the bin to where people are. Think fruit flies first and a distant second drain flies. Google then click images to see lots of pictures to make your determination. To get rid of them think vacuum cleaner, sticky trays, vinegar traps, stop feeding, bedding inches thick on the bin, thin cloth covering the bin. Fruit flies I can casually dip out of my wine glass. Drain flies bring out my killer instinct. Do drain flies actually infest worm bins? They may damp plants.

What you are seeing is fruit flies that are attacted to the worm food that is rotting. Ensure that their is plenty of bedding covering the food.

They may be fungus gnats. The can be hard to control. A no pest strip in the room for a couple of weeks should get rid of them. You will need time for their eggs to hatch so you get the babies too.

The chickens love the fruit flys, as far as I know they are simply another decomposer so for my outdoor worms they present no harm though I could see where they would be undesirable in an indoor worm bin.

Every option I could think of to deter them was in Equinoxs post, the two I would try first are cheesecloth cover to isolate them but still allow airflow and vinegar and my thought there was a mist to spray things down when the cloth cover is removed for adding food to the bin.

Yes most likely is fruit flies. What I did was put some apple cider vinegar in a dish and add a couple drops of dish soap, cover with saran wrap , poke small holes for them to enter and they will drown in the mix. Works like a charm.

I realize this thread is over a year old, but it seems to be just what I need. Found tiny gnats in my worm factory today. Did you put the container holding the vinegar/soap cocktail near your worm bin or in it?

Yes, when I had the fruit flies I put the vinegar dish near and even on the lid of the bin. Really its pretty easy to tell fruit flies from gnats as they fly. FF are fast darting from here to there, gnats are slow sort a floating easy going gait. Since I start cuttings every winter for plants I have both inside so I have my share of the sticky cards and vinegar solution.

I've never gotten fungus gnats to get attracted to vinegar any more than they are attracted to cups of water. Both will accumulate some drowned gnats, but neither does all that much.

Fungus gnats are harder to control than fruit flies, as their larvae feed off of the compost itself, and adults seek out wet soil with high organic content--vermicompost is basically the ideal nursery for them. I've seen them try to literally dive-bomb into the moist dirt when I repot plants. Luckily, they haven't gotten into my worm bin (yet), but I've had them in my plants and seedlings. Huge annoyance and, in the case of seedlings, the maggots can eat so much of the developing roots that it permanently stunts the growing plants.

In my plants, I drench with hydrogen peroxide, which kills the larvae, but I wouldn't do this in the worm bin for fear of hurting the worms.

Something with BTi (Bacillus thuringiensis israelensis) such as Gnatrol, Mosquito Bits, Knock-Out Gnats, etc., will kill the fungus gnat maggots. With regular application, you stop the life cycle, but the adults do not die immediately, so you might want to supplement with sticky traps, etc. Not sure whether this is effective on fruit flies. It will not hurt your worms.

Note that BTk (Bacillus thuringiensis kurstaki) is not effective on fly or gnat maggots or mosquito larvae. It's used on caterpillars and grubs.

The vinegar is an attractant for fruit flies not gnats.

Yes, but people often conflate fruit flies and gnats. The recommendation to use vinegar for fungus gnats is all over the internet, so it's worth emphasizing that it doesn't really work on them.

Couldn't find Gnatrol, but was able to find Mosquito Bits. Going to give that a try, along with the sticky traps.

It's possible the BTi will not work on fruit flies, if you have/also have those. It seems to get used primarily on Nematocera (long-bodied fly suborder, includes mosquitoes, fungus gnats, black flies, etc.), and fruit flies are in suborder Brachycera. So make sure you identify what exactly you have to find the best strategy.

Will the mosquito bits contaminate the compost from the worms? Could I still use it for my garden?

@Angelia Howard I would think the castings would still be fine. BT is organic. I'm about to treat my bin. I was worried about killing the worms or their eggs. I can't Find Any information on it.

I've foudn best way to control all flying insect probs in bins is a thick layer of dry shredded paper on top. it'll eventually get incorporated into the bin, worms love it as a place to hide when conditions elsewhere not to their liking. Add more when the top noticeably deteriorates, gets wet or changes colour./

I teach worm composting and if you have flying insects prepare new bedding and put it on top and do not feed for 2 weeks.

When you have gnats or fruit flies, cover with new bedding and do not feed for two weeks.