The common name fruit fly is often used to describe small ( ~ 3 mm) flies with bright red eyes in the family Drosophilidae (a.k.a. vinegar or pumice flies). Larger flies sporting spotted or banded wings in the family Tephritidae attack fruit and other plant parts also go by this name. Details of the former will be investigated today and strange dealings of the latter await another episode.
Over the past week or two I have received many questions about hordes of tiny fruit flies buzzing around fruit bowls, kitchen sinks, and counters tops. They seem to appear from nowhere and lend credence to Aristotle’s notion that living organisms like tiny flies can originate spontaneously from non-living or putrefying things such as decaying organic matter. Now famous experiments by Francesco Redi and Lazzaro Spallanzani pretty much disproved Aristotle’s theory of spontaneous generation, but the appearance of all those tiny flies remains vexing even for bug geeks.
To help untangle this mystery, consider the recent weather. This autumn has been particularly damp in the Washington metropolitan region by virtue of hurricanes, tropical, storms, and incessant weekly showers. These warm moist conditions are nearly ideal for the decomposition of tons of leaves, fruits, and other vegetable matter that have accumulated during summer and early autumn. My compost pile is a writhing mass of invertebrates intent on converting vegetable protein into animal biomass as quickly as possible. A cloud of fruit flies hovers over my compost pile each day. Near my front door resides a pumpkin with yet another swarm of fruit flies dining at a squirrel inflicted gash in the pumpkin’s flesh.
Between the battalions of fruit flies breeding in my compost and the squadron of flies at the front door, undoubtedly one or two raiders can infiltrate my home each time the door opens or closes. Once inside, yeasty odors of acetic acid and ethanol emanating from an over ripe banana in my fruit bowl serve as powerful attractants for the flies. After arriving at my squidgy fruit, the female fruit fly deposits eggs. Each gal deposits on average roughly 500 eggs during the course of her life time. Small translucent larvae hatch from the eggs. They glide through the overripe fruit slurping-up nutritious fermenting fluids as they develop and grow. When ambient temperatures are warm, as they have been for the last several weeks, fruit flies can complete a generation in less than two weeks. With their capacity for reproduction, populations around the fruit bowl can explode seemingly overnight.
Fruit flies may also enter your home as stowaways, if you purchase overripe fruits or vegetables from the market that harbor eggs or tiny larvae. Inspect your produce carefully and wash fruits and vegetables. If fruit is unrefrigerated and displayed in a bowl, check it out regularly and toss over-the-hill items before they generate flies. Fruit flies can also breed in sink or floor drains, garbage pails, or recycling containers in homes, restaurants, and offices where decomposing organic material accumulates. Inspect these areas regularly, clean up spills, and disinfect surfaces.
For the cloud of fruit flies wafting around your home, consider building a vinegar trap to catch and kill them. These traps can be purchased commercially and several trap designs are available on the internet. My vinegar trap consisted of an 8 oz clear plastic tumbler filled with 4 oz of wine vinegar and a few drops of dish detergent. Within 24 hours more than 100 fruit flies were lured to their death. ‘Twas not the fruit that killed the beast, only the fragrant promise of an overripe banana.
We thank Liz and her buggy bananas for providing the inspiration for this episode. The interesting references “Trapping spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), with combinations of vinegar and wine, and acetic acid and ethanol” by P. J. Landolt, T. Adams, and H. Rogg and “Flies, gnats, and midges” by W. A. Kolbe in “The Handbook of Pest Control” were used in preparing this Bug of the Week.
For more information on fruit flies, please visit the following web site: