Over the past few days there have been dozens of small flies gathered in the corners of the kitchen windows. They seem to spend much of the day walking around on the windowpane, but every so often one will fly off with a slow, almost ponderous, tail-heavy flight. Numbers are most concentrated around the fruit bowl, something that underlines the fact that these are Drosophila fruit flies, small insects with which many students of biology will be familiar. Another name that is sometimes given is vinegar fly and this might explain the way in which they are drawn to the wine glasses over dinner. It seems that I am not alone in receiving this visitation; similar reports from across the county have been posted on local wildlife forums and the flies have already made it into the local paper.
According to Tony Irwin, writing on Dipterists Forum, most of the flies involved are a species called Drosophila melanogaster but smaller numbers of a related species are also involved. Drosophila melanogaster is an interesting fly because it is one of the most studied organisms in the world, being used as a model subject in the field of genetic research. One of the main reasons for its use in the study of genetics is its remarkably short generation time. At roughly two weeks per generation, this means that many generations can be studied in a short period, allowing the effects of genetic manipulation (e.g. by cross-breeding) to be studied readily in the laboratory. Two additional features of particular use to researchers are that the females produce lots of eggs over the course of their lifetime (some 2,000 according to some studies) and that the males and females are easy to distinguish from one another. Mind you, since the flies are just 2.5 mm in length, you need a magnifying glass to spot the male’s dark abdominal patch and sex-combs. The latter are a series dark bristles on each of the front pair of legs.
Fruit flies have been an important research tool in laboratories across the world. Rightly or wrongly they have been used to study the effects of radiation, with researchers documenting the effects of different radioactive doses on the behaviour and body morphology of subsequent generations. Associated with this wider work has been Cornelia Hesse-Honegger, whose paintings of fruit fly mutations are both amazing and, at the same time, somewhat shocking. Cornelia has also used a similar approach to document the potential legacy of Chernobyl on other insects and plants, charting mutations and deformities that would otherwise be overlooked. Certainly when you are working with such small creatures, you do need an eye for detail.