A simple, nontoxic, inexpensive, humane way to trap them is to place a banana peel inside a clear plastic container and make three or four holes in the cover with a standard round toothpick. Be sure to pull the toothpick all the way through the plastic and wiggle it around to make a hole large enough for a fruit fly to crawl through. Place the plastic container in or near the fruit bowl, not inside the worm bin. (If the worm bin is not in your kitchen, place the fruit fly trap on a surface above the worm bin; if it is inside or too close to the worm bin, the odor of the banana peel will not be distinct enough to attract the fruit flies as effectively). Within 24 hours, about 99 percent of the fruit flies will be inside the plastic container, having entered the holes and not found their way out. Each day, take the container outside and release the fruit flies, unless you are a biology teacher or entomologist and want them for genetics experiments. After three or four days, the fruit flies will be gone (if no additional banana peels or other potential source of larvae have been added to the worm bin).