To help untangle this mystery, consider the change of seasons.  Autumn in many parts of the country is characterized by damp cool weather by virtue of incessant weekly showers. These moist conditions are nearly ideal for decomposing tons of leaves, fruits, and other vegetable matter, the accumulated bounty of Mother Nature’s efforts during spring, summer, and autumn. This week of early November my compost pile is a writhing mass of invertebrates intent on converting vegetable protein into animal biomass as quickly as possible. On warm days a cloud of fruit flies hovers over my compost pile and some of these winged raiders undoubtedly infiltrate my home when the door opens. Like many kitchens, mine is home to a bowl of fruit that occasionally contains one item that has gone a little squidgy. Yeasty odors of acetic acid and ethanol emanating from an over-ripe banana serve as powerful attractants for fruit flies. After arriving at the banana, the female fruit fly deposits eggs. Each gal lays roughly 500 eggs during the course of her lifetime. 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, 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 can also enter your home as stowaways when you purchase overripe fruits or vegetables from the market. These goods may arrive preloaded with a complement of eggs or tiny larvae. To reduce chances of bringing home an infestation, 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 these noisome rascals.  Traps can be purchased commercially, and several trap designs are available on the internet. My DIY vinegar trap consists of an 8 oz clear plastic tumbler filled with 4 oz of wine vinegar and a few drops of dish detergent. Within 24 hours of placing the trap on the counter, more than 100 fruit flies were lured to their death. Stealing a line from Robert Armstrong of King Kong fame (RKO, 1933) “Oh no, it wasn’t the banana that killed the beast. It was the fragrant odor of yeast.”