It's late summer and there are lots of tiny flies in your kitchen hovering around overripe fruit. They are probably fruit flies — also commonly called vinegar flies. They aren't considered harmful but they can be a real nuisance.
Biology and Habits
The fruit flies in your kitchen are the same ones used in science labs to study genetics. Drosophila melanogaster (as they are called) are ideal because they breed prolifically during a short life span and are easy to "raise."
These red-eyed fruit flies are small — about 1/8 inch long — and have tan bodies with black on the rear portion. A female lays about 500 eggs (and up to 2000 eggs) near the surface of moist decaying food. Tiny maggots (larvae) hatch within 30 hours and feed on yeast found in the fermenting liquid. The maggots move to drier areas to pupate and emerge as adult flies in less than a day. Within two days, the flies are ready to mate. Depending on the temperature, it takes only eight to 15 days to complete the entire life cycle.
Most likely the fruit flies arrived in your kitchen on already infested food such as overripe fruit or tomatoes with split skins. They may also have come in through windows or doors.
Prevention and Control
The only sure way to control fruit flies is to locate and eliminate potential breeding places. Sometimes the problem is obvious but in other cases it can be challenging to locate the breeding sites.
- Fruit flies are attracted to ripe and overripe bananas, melons, tomatoes, squash, and apples, as well as rotten potatoes and onions. Store fruits and vegetables in the refrigerator until the fruit fly infestation is under control. Check for food scraps hidden under furniture or elsewhere.
- Discard rotten food in an airtight container until you can dispose of it in an outside garbage can. When the decayed area is small, it's fine to cut it off and discard just the bad part. Because fruit fly eggs and larvae are found only near the surface, you don't need to worry about a hidden (deeper down) infestation of eggs or larvae.
- Food debris or liquids are potential breeding sites, so clean the garbage can and rinse out wine, beer, juice, and pop bottles before they go into the recycle bin.
- You can detect infestations coming from kitchen drains and disposals by taping down a piece of clear plastic over the drain hole and leaving it in place overnight. In the morning, look for flies waiting to get out. (If the flies look fuzzy or hairy, they are "drain flies" and not fruit flies.) Use a brush to clean the scum off drain pipes and rinse with boiling water. Clean disposals according to operating instructions.
- Window and door screens using 16-mesh screening will keep fruit flies out, but they also need to fit snugly and be in good repair. Newly emerged adult fruit flies are attracted to light so they may be attracted to lights over windows or doors. You can consider using special yellow lights or reduce the use of lights over windows or doors.
You'll want to start trappping fruit flies right away to reduce their numbers. Cosmetically enhanced fruit fly traps are available for purchase, but you can easily make effective traps at home. Try these suggestions:
Bowls. bottles or other containers can function as open traps. An effective baiting solution consists of 4 Tablespoons (1/4 cup) or 1/2 inch worth of apple cider vinegar or wine plus a few drops of dishwashing liquid. The dish detergent affects the surface tension of the liquid and fruit flies that land on it will drown.
Closed-up traps consist of three components — an empty jar, an attractive bait inside the jar, and a cover secured to the top of the jar to prevent escape. The cover, which can be plastic wrap, a sandwich baggie or a paper cone, has one or two small holes that are no more than 1/8 inch wide. After fruit flies enter the jar through the hole, they usually don't find their way out again.
Bait Recipes for enclosed traps:
- 1/4 inch of apple cider vinegar or wine. Beer may also work. Replace bait as needed.
- Pieces of attractive fruit. Bananas or other fruits that attract fruit flies will make good baits. The bait may lose it attractiveness quickly, so try putting out a new trap daily, alternating between two jars. This method is a good choice for for people who don't like the smell of vinegar.
- A yeasty mixture: In the bottom of the jar, dissolve 1 package of yeast (about 2 tablespoons) in 1/3 cup warm water. Add 1 teaspoon of sugar and mix gently. This mixture can last a week.
Jar Coverings for Enclosed Traps:
- Secure a piece of plastic wrap over the jar using a rubber band. Poke one or two small holes using a toothpick or pencil. (You can enlarge the holes if fruit flies do not enter the baited jar.)
- Poke a hole in the corner of a plastic sandwich baggie. Create an inverted cone inside the jar by orienting the corner hole at the low point of the cone. Secure the baggie to the jar with a rubber band.
- Create a cone with a regular sheet of paper leaving a small hole (1/8 inch) at the bottom. Tape the outside overlapping edge to secure the cone's shape. Put tape around the top of the jar so that half of it extends above the top edge. Insert the cone in the top of the jar and carefully press tape to both the cone and the jar to seal escape routes.
When the trap has lots of flies, you can take it outside and release the flies by removing the plastic covering or paper cone. Or you can kill and dispose of trapped flies by immersing the entire trap in a pan of hot soapy water, removing the covering to let the jar fill with water. The soapy water (along with the dead fruit flies) can be poured down the drain.
You'll be surprised at how quickly you can reduce fruit fly numbers within two or three days by focusing on trapping.
Lyon, WF. 1997. Vinegar Flies. HYG-2109-97. Ohio State University Extension. http://ohioline.osu.edu/hyg-fact/2000/2109.html
Ogg, B. 2008. Managing Fruit Flies: Make Your Own Trap. Unversity of Nebraska-Lincoln Extension in Lancaster County.http://lancaster.unl.edu/pest/resources/FruitFlyTrap.shtml
Potter, MF. 1994. Fruit flies. Entfact-621. Univ. of Kentucky Cooperative Extension. http://www.ca.uky.edu/entomology/entfacts/ef621.asp
Rumsey, Kay. "Fruit Flies (Vinegar Flies)", NCAP