Let's start first with prevention:
- Make sure your compost scraps are covered (especially in the summer). This is especially important if your scraps are kept near a window.
- Bury all food deep in your worm bin and keep the bedding layer at least 3 inches deep.
- If you have fruit flies in the kitchen or where you keep your compost scraps, assume they are laying eggs on the compost scraps. Either freeze the compost scraps or take them to your outside compost pile.
Dealing with an infestation **First know that fruit flies have a life cycle and there is an end to the problem.** The quickest way I’ve found to deal with fruit flies is as follows:
- Remove adult fruit flies from your worm bin and nearby area. You can do this by vacuuming them, using sticky traps, or vinegar traps. You’ll need to vacuum them at least twice a day for 2 weeks to be sure you get all the adults from the eggs of the generation you first removed. Sticky and vinegar traps should be monitored and replaced when needed.
- Make your worm bin less attractive to the flies. This means not adding more food to your bin until your infestation is under control. Your worms can go without food for a few weeks. Fruit flies cannot.
- Make your bin more dry. Slightly dry bins are less prone to develop flies (addresses a potential pH problem). You are not looking to make a BIG change here only a slight change in dampness. Adding freshly shredded newspaper to the BOTTOM layer of your bin will do the trick. Alternatively, you can upend the contents of your bin and add more bedding over the former bottom contents.
- Fruit flies need to fly to mate-- if you fill your bin with newspaper that will also help.
- OPTIONAL... I read a tip earlier this year from a fellow vermicomposter (in Australia!) who uses diatomaceous earth (DE) to control flies. Flies are VERY bad in Australia apparently. I have not tried it, but you can get DE from garden centers (or ACE Hardware). DE kills insects and it won't hurt worms, plants or you. I think it is worth a try in combination with the other steps. If you have used DE, let me know how it worked and how much you used.
If you follow these steps you will be free of fruit flies in a few weeks. The most important things you can do are bury your food and kill/remove the adult fruit flies.
Originally published on September 4, 2008