DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > ASCHIZA > Platypezoidea > Phoridae (356 species)

(subfamilies: none)

A particularly large family of small, solidly-built, mainly dark-coloured flies that typically have an enlarged, somewhat arched thorax, giving them a characteristic humpbacked appearance. They are commonly found on or in the vicinity of decomposing vegetable or animal matter, faeces, fungi, or around ant and bee nests. In conjunction with their reasonably distinctive appearance, the adults are recognisable by their quick, jerky movements as they scuttle about on leaves. The larval biologies of the family are extremely varied and complex.

Phorid flies are further described as being minute to medium-sized (0.5-6mm), with a body colour that varies greatly from black through brown, orange and yellow to pale grey; head, palps and legs usually with strong, dentate or feathered setae; eyes dichoptic; antenna with a large, rounded or elongate third segment bearing a long apical or somewhat dorsal arista directed sideways; wings clear or tinged, rarely with markings; venation reduced, with the strong radial veins ending in the costa about halfway up the wing; the other veins are weaker and usually follow a diagonal course, often parallel to each other; legs typically with stout femora; hind femora often somewhat laterally compressed.

Although I think it would be fair to say that, in the past, any member of this particular family would have to be examined under a microscope to confidently determine the species or even the genus, that is not necessarily the case now with well-detailed photos. Of course, you have to have the knowledge of what to look for, which I certainly don't have, but there are experts who have a specific interest in certain families and are able to provide some level of identity. In this respect, Dr Mark Welch (NHM) has carefully inspected the photos featured below and has kindly provided the following comments.      

The copulating pair that I photographed in Devon are Phora sp. If you look closely at the mid tibiae of the male you will see a few slender dorsal bristles that form part of a row (usually of 4-5 bristles); you can see two on the right mid tibia (other dorsals have been lost) and three on the left mid tibia (partly obscured by the female's hind metatarsus). Although not visible here, Phora also have a missing R2+3 vein (no fork) and R1 and R3 are strong and black. Phora also have big eyes with a very narrow gena below, which is fairly distinctive. In general, Phora identification is based on the males only; entailing careful microscopic examination of the hypopygium (modified ninth abdominal segment that includes the copulatory organ known as the aedeagus), which first has to be removed, cleaned and mounted. Consequently, identification to genus is as good as it gets from photos.

I initially thought that the phorids I found on a small clump of honey fungus in the New Forest were likely to be Megaselia halterata, commonly known as the fungi phorid, but I was wrong. Mark confirmed that Megaselia lack non- apical bristles on their legs, although they can have other hairs, which he explained in detail. The individuals I photographed lack a hair palisade on the hind tibia, but do have one weak short dorsal bristle on the fore tibia, a posterodorsal/anterior pair of longer bristles on the mid tibia and an anterodorsal bristle on the basal half of the hind tibia. These features are apparently typical of Triphleba. Other features consistent with Triphleba are the thick R1 and R3 veins and strong R2+3 vein. None of the photos I initially posted to the Diptera FB group had sufficient detail of the male hypopygium. However, the combination of yellow legs, pale halteres, black head, black thoracic dorsum, black tergites and the dark underside suggested Triphleba luteifemorata - a common species that could have simply been using the fruiting body as a platform for mating. There is one species in the genus though whose larvae are recorded as fungivorous, which is Triphleba minuta and, fortunately, that species was subsequently confirmed when I posted further images that showed a clearer view of the male's genital capsule and, most importantly, a 'rootless' R2+3 vein (the small fork off R3). The amount of detail here that had to be checked shows why most of these species are left as 'unidentified'.

The only other species that I'm currently able to feature, which I photographed in the garden during the winter, was identified as Triphleba papillata, duly determined by a combination of characters, which included four scutellar bristles (three present and a scar where one is missing), black haltere, complete R2+3 fork, orange fore tibia and mid and hind legs with orange 'knees'. Also, the seventh sternite as they can be very distinctive in most female Triphleba. Mark kindly annotated my photos to clearly show the key features, which I obviously found interesting as it helped me understand everything he said, but it also showed me that there's no way that I could have keyed the species out in this manner.

One final note, is that whilst I mentioned Megaselia, I didn't comment on the fact that it is an absolutely enormous genus with close on 260 species and, not surprisingly, has its own dedicated 'key'. The remaining species are placed in 22 genera with Triphleba and Phora being the two largest with 24 and 13 species respectively.

Updated Nov.24 (v.2)