This is the time of year when old tomatoes, peaches or spoiling bananas sit on the kitchen counters at home. Our home being no exception, fruit flies become so plentiful I decided to investigate their life cycle.
I set out to capture several flies so they could be photographed to illustrate this article. An extremely fine mesh net I had make many years ago to catch butterflies was put to the test. Initially, I captured two flies only to watch them wiggle through the net and quickly disappear. Finally, I discovered after netting one, that if the net was placed on the counter with a glass jar over the fly and net, I could watch the fly escape into my jar to be photographed later. A feeling of admiration for these pesky insects overcame me so I affectionately considered them tiny rascals.
My wife knows fruit flies can be attracted to a solution of vinegar and dishwashing detergent. Normal water surface tension supports and allows some insects like water spiders to walk on water without their legs breaking through the water surface. Since detergent decreases water surface tension, when the fly lands on the solution its legs sink into the vinegar where it drowns.
The common fruit fly is actually a vinegar fly. This image was taken in the author’s kitchen. When observed in nature, the vinegar fly has yellow and black bands on the abdomen and bright red eyes, creating a most dapper appearance. Illumination of the vinegar fly produced a long shadow.
Interestingly, I learned the common fruit fly present in this country is actually a vinegar fly called, "Drosophila melanogaster." True fruit flies differ from the common vinegar fly in that true female fruit flies puncture fresh healthy fruit to deposit eggs. The eggs develop into tiny maggot-like larvae which burrow into fruit. Microorganisms like bacteria and fungi enter the pathway made by the larvae to feed on the fruit. The larvae of the fruit fly actually eat the microorganisms and not the fruit. By contrast, the common vinegar fly female lays her eggs on decaying or spoiled fruit. The decay and spoilage process occurs as a result of microorganism (bacteria and fungi) action, hence, the vinegar fly larvae will feed on available microorganisms but not on the fruit itself. Just this week I noticed small larvae wallowing in spoiled cherry tomato juice on the bottom of a wooden quart container in my kitchen.
Vinegar flies are considered harmless, but the text book, "The Common Insects of North America," states that swallowing the larvae of flies may cause myiasis, a disease of the body cavities cause by the larvae of flies, so spoiled fruit should be disposed of.
The common vinegar fly is considered a most well known organism since it is found wherever spoiled fruit exists throughout the world. Its habitat is considered cosmopolitan. Close-up, the vinegar fly has two wings overlapping the body. The adult fly measures 2.5mm in length while the larva is 5mm in size. When observed under a magnifying lens or through the macro camera lens, yellow and black bands on the abdomen and the bright red eyes create a dapper appearance.
The female vinegar fly may lay up to 2,000 eggs which develop into mature adults in 2-3 weeks. Since the vinegar fly is easy to grow on laboratory food medium, has a rapid short life cycle, and is prolific with 20 generations in one year, the species has been used for laboratory experiments in genetics and molecular biology for 90 years.
It has been nickname, "the laboratory rat." In my college genetics class 50 years ago red-eyed vinegar flies were mated with brown-eyed vinegar flies to observe the number of red- and brown-eyed offspring which taught dominant and recessive gene expression. In the 1920s vinegar flies were exposed to x-ray radiation to cause gene mutation. These experiments contributed to knowledge of the molecular and chemical composition of genes on chromosomes of the vinegar fly.
The tiny rascal in the accompanying photograph, while a nuisance in my home has lead scientists to monumental discoveries and understanding of the natural world. Try capturing one of these vinegar flies in a jar, then observe it close-up under a magnifying lens. The vinegar fly is beautiful.