DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > SCHIZOPHORA > Acalyptratae > Ephydroidea > Drosophilidae (65 species)

(subfamilies: Drosophilinae and Steganinae)

The members of this family are generally regarded as persistent, small nuisance flies that may be seen congregating around compost bins or in the vicinity of the larval habitats of decaying vegetation, plant sap, fungi or, more often, on overripe or rotting fruit. The presence of these flies at home is a good reason to check the fruit bowl, because once fruit has begun to spoil, the fermentation process has started, which attracts the flies by the feint smell of alcohol. It's the same reason that they can be drawn to glasses and open bottles of wine or beer. However, it's important to remember that they're not all nuisance species as the majority are of no real concern and, certainly in respect of one species as noted below, are actually beneficial.

The common name of small fruit fly tends to indicate that they are small tepthritids whose larvae develop in the tissues of living plants, which of course is confusing, which is why they are starting to be called vinegar flies on the basis that they can literally turn wine to vinegar. Another name is pomace fly, but that's mainly used in the US. Interestingly, Drosophilidae means 'lover of dew' so I'm not sure where the common name originated.  

Family characteristics are given as, minute to medium (1-7mm) flies; dull or lustrous, with body colour varying from yellow to brownish black, often with some whitish markings on head and thorax and/or a pattern of stripes on thorax and abdomen; eyes often clear red; arista usually with long rays, in some cases pubescent; ocelli present; ocellar bristles present, except in Acletoxenus; postvertical bristles usually present, converging; three pairs of frontal bristles, one pair curving forward or obliquely inward and two pairs backward; scattered interfrontal bristles present; vibrissae present; wings usually unmarked, in some cases with dark markings or extensively infuscated; costa with humeral and subcostal breaks; tibiae virtually always with dorsal preapical bristle, sometimes small.

The best known, and most documented fly in the family is Drosophilia melanogaster, a species which has been studied around the world in biological research, particularly with regard to genetics and the development of tissues and organs in the fight against cancer. The Wikipedia article on the species is an extremely lengthy, but fascinating read in this respect. The species can be distinguished from various features, but one that is particularly visible, quite literally, is their large eyes where the gena is no more than a tenth of the diameter at its greatest height. These large eyes are particularly sensitive to any slight difference in light intensity and, as such, they will instinctively take flight if they detect movement or shadow.  

In stark contrast, Drosophilia suzukii has become a serious pest species as it damages ripening soft fruits, such as strawberries, raspberries, blueberries and blackberries, as well as grapes, cherries, peaches and plums. The other species that are associated with fruit are mainly attracted to fruit that has already started to rot, whereas with this species the female specifically targets unblemished fresh ripe fruits by using her saw-like ovipositor to lay her eggs under the skin. The larvae then grow and hatch within the fruit thereby destroying its commercial value, which is now causing very significant economic loss in many soft fruit crop-growing areas, especially in the US and Europe. The adults are small, around 3-4mm, with a yellowish-brown thorax and relatively large red eyes. The males have a conspicuous brown smudge on the wings at the tip of vein R2+3. The females lack this distinctive marking, which obviously makes identification more difficult. I think that the individual featured here is correct, particularly as it's on a fresh wild blackberry, but I can't be sure as there are some other similar species.

Unfortunately, I have very few photos of these species.

Updated Nov.24 (v.2)