Tales of the Drosophila: Preventing Uninvited Guests

Possibly the presence of fruit flies is no big deal for composters in other parts of the country where they keep a bin in a utility room or something. Yet, to those of us living in cramped New York apartments, these hovering slow fliers can be a major pain! As Frank Teuton describes, drosophila are truly the “bete noire” of indoor vermicomposting. The urban composter is not helpless: There are options. Fruit fly eggs and larvae are found the skins/rinds of certain “tropical” fruits such as bananas, citrus fruits, pomegranates, avocados, etc. To destroy these eggs and larvae that live on the peels—and prevent fruit fly infestations—a good rule is to freeze or microwave food waste prior to placing it in your bin. Others even boil the problematic fruit additions.

[Also, don’t overdo citrus peels in the worm bin as the can irritate the worms’ skin. For an indoor bin, that means no more than one added per day.]

You can freeze the food waste overnight or until you are ready to add it to the bin.

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 three inches deep. Also, keep the food waste under several inches of bedding. Several sheets of damp newspaper or landscape fabric act as a barrier to odors, which will help to prevent attracting fruit flies. It will also reduce their access to the bedding below. (Hold off on dampening your paper bedding as food waste that has been frozen will cause extra dampness in the bin, and particularly in the bedding.)

For those with outdoor compost bins: If fruit flies become a nuisance, your ratio of food scraps (wets) to high carbon material (dries) is too high. Make sure high carbon materials, such as brown leaves, shredded paper, or cardboard comprise at least 50% of the bin’s total material. Keeping about a one foot height of high carbon material on your pile’s surface above the food scraps should do the trick.

One can find many examples of fruit fly traps on the web, but they are an action of last resort. An example of such a “trap” uses a liquid attractive to fruit flies, such as vinegar, wine, soda, or fruit juice. Put a few ounces of "bait" into a jar or cup and attach a plastic bag on top with a rubber band. Then, cut a few small holes in the plastic bag. The flies go in, but don't come out.