Troubleshooting
If environmental conditions are kept tolerable for the worm population, any possible problems that could develop will likely relate to the presence of other organisms in the bin. These will usually cause no heartaches for the worms but could be a nuisance inside a household.
Fruit flies often come in with the fruit and vegetables we purchase at the store. These materials may also have fruit fly eggs on them which will hatch given the right conditions. Fruit flies can be mostly prevented by freezing the food scraps before putting them in the bin. This will kill any fruit fly eggs that are on the food. In addition, freezing breaks down the cell structure of the material, and it will eliminate things such as carrot tops sprouting in the bin. After food is frozen simply withdraw it and bring it back to room temperature before adding it to the bin.
Fruit flies may also come into the bin from other places. A well sealed bin lid and only a minimum of small ventilation holes will help to prevent their occurrence. If present however, one documented method to deal with them is to place beer in a small glass jar or bottle inside the worm bin. A small plastic bag with a hole in the bottom is folded atop the jar and secured to the rim with an elastic band. The hole in the plastic bag should be located just above the surface of the beer. Fruit flies will be attracted to the beer, fly through the hole, and hopefully, drown.
Other organisms, such as fungus gnats and mites may also be present that are not attracted to beer. One method that may be attempted to deal with these is to place a thick layer or dense bedding material, such as sterilized topsoil, over the entire surface of the bedding material in the bin. To present attraction of these other organisms in the future, fresh food wastes added to the bin should be buried deeply within the bedding material and covered immediately.