The Problem: Fruit flies in your vermicompost bin or in your pre-composting container.
The solution for both of these problems is super simple.
If you are finding fruit flies in your worm bin simply stop feeding. Cover the exposed surface of the bin with coffee grounds. Then add a layer of fresh bedding. The easiest fresh bedding is shredded paper spread 1/2 inch deep over the surface. Torn newspaper or egg cartons could also be added or mixed in. You won’t need to wet it down, it will be damp in just a few days by wicking excess moisture from the bin.
Wait a week then check the bin for fruit flies. If the flies are gone you can start feeding the worms again, but be very conservative with the amount at first. For a moderate-sized bin 1/4 cup every few days. You can increase this amount slowly over time. If you start to get flies again stop feeding until the flies go away. Increase the amount you are feeding until you are just below the previous high water mark. Over time you should be able to feed more but even a mature bin can have problems with overfeeding. Pay attention and you shouldn’t have any trouble.
Dig in the bin a bit before feeding. If the majority of what you put in last time is still there, then wait before adding more food. Freeze excess food. This helps break it down and makes it easier for the worms to process quickly. Make sure you thaw completely before feeding to the worms. Anything you put into the bin should be room temperature.
Freezing is also the best solution for stopping fruit flies in a pre-composting container. A pre-composting container or kitchen bin is the collection spot for kitchen scraps before they are fed to the worms or taken outside to be added to a conventional compost pile. Place the scraps in a large ziplock bag and stick it in the freezer (clearly labeled). No fruit flies and the freeze-thaw cycle will help break things down faster.
Composting is a lot more fun if you aren’t hatching fruit flies in your house.