We have a problem with what seem to be fruit flies, but we don’t have any fruit sitting around in the house. I can’t figure out where they’re coming from but this has been going on for weeks. Any suggestions? L. K., Newburyport, MA

First, you need to make sure that you are dealing with fruit flies. There are other similar small flies that breed in somewhat different sites (see Tracking Down Indoor Gnats). A professional exterminator could identify your flies and inspect for breeding sites.

Fruit flies (Drosophila) can be developing in lots of different hidden places. The tiny maggot-like larvae feed in a variety of wet, fermenting, vinegary, or overripe foods. The infestation often starts with infested fruit but then emerging flies can find new breeding sites elsewhere in the house. They can also enter from outdoors, especially if there is rotting fruit outside (see Fruit Flies Can Come From Many Sources).

It doesn’t take much food or spillage for fruit fly larvae to develop into adult flies.

Check These Places for Developing Fruit Flies

• Overripe or bruised fruits such as bananas, strawberries, tomatoes, or pineapple that are unrefrigerated and left sitting out on counters

• Bags or bins of rotting vegetables such as potatoes or onions in pantries or stored under sinks, closets, or in the garage

• Trash or garbage cans, especially underneath plastic bags that have leaked into the bottom of the container

• Recycling bins with spillage in the bottom, unrinsed food containers, or bins containing wine, beer, or soda bottles with liquid remaining

• Decaying food spillage hidden under refrigerators, stoves, counters, or under the sink.

• Dirty drip pans under refrigerators, humidifiers, air conditioners

• Discarded, partially empty containers of fermented or vinegary foods such as wine, beer, vinegar, cider, pickles, ketchup

• Scummy drains in sinks, tubs, or floor drains

• Soggy mop buckets or damp mops and cleaning rags

Photo Credit : “Drosophila repleta lateral” by Bbski – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.