Adult small fruit flies are 1/8 inch long and cream or yellow to dull medium brown in color with red or orange eyes. Dark-eyed fruit flies are slightly larger and heavier bodied and darker in color all over with dark brown eyes. Larvae of each are tiny cream-colored maggots that can be as long as 1/4 to 3/8 inch with no eyes or legs. Pupae are about the size of the adults and light tan.

Small fruit flies are also called vinegar flies because they lay eggs at the surface of fermenting or rotting fruits and other foods, as well as in wet mops, garbage cans and recycling bins, food containers, and any fermenting substance or liquid. Eggs hatch quickly and larvae feed on the yeast, causing decay. Within 5 days the larvae move to a drier spot and pupate. Small fruit flies reproduce very quickly. The dark-eyed fruit fly is not attracted to yeast or fermentation but the bacterial slime that develops in drains, cracks, and crevices around food service areas. Larvae develop in the slime and feed on bacteria.

Small fruit flies are common in restaurants, bars, homes, composting areas, and recycling areas or containers, and can be found anywhere outdoors. They are a nuisance but also indicate an issue with rotting or decaying foods or liquids, such as wine and beer. The dark-eyed fruit fly, on the other hand, is a frequent pest of restaurants, bars, and catering halls, and indicates a lack of sanitation in or around food-handling areas or a bathroom. They will land and linger on walls close to breeding sites, which can be aesthetically unpleasing to customers.