DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > SCHIZOPHORA > Acalyptratae > Carnoidea > Chloropidae (178 species)

(subfamilies: Chloropinae and Oscinellinae)

A large family of tiny to small-sized flies that are extremely difficult to identify from photos. Most of the species you're likely to encounter will probably average around 2-5mm body length, but there are others that are smaller, some of which are barely more than 1mm, and a few that are a tad larger. They are also rather variable in both form and colour with a body that may be short and stout, slender or elongate; typically, either black, or yellow-brown to bright yellow in colour, sometimes with red or brown markings, and often shining due to the general absence of hairs; the head is variable in shape, in most species with a broad frons that usually has an enlarged, sclerotised, plate-like ocellar (frontal) triangle that is often sharply margined (although in some species difficult to distinguish), delimited from the frons by colour or banding and with a surface varying from smooth and polished to densely pruinose and dull; thorax finely haired, with a sharp lateral carinate margin to the propleuron, and with a scutellum that may be short and rounded, elongate, conical or flattened; abdomen broad and tapering; the wings are generally clear with reduced, but mostly consistent venation throughout the family, a subcostal break, and a kink in the CuA1 vein where the crossvein m-cu would have been, albeit a feature that is often hard to see; importantly, the extent of the costa separates the species into two distinct subfamilies - Chloropinae where it effectively terminates at or around R4+5 and Oscinellinae where it is longer extending to, or very close to, vein M1+2.

Although chloropids are mainly encountered in open grassland areas, some species are more likely to be found in woodland clearings or various wetland habitats. The larvae generally feed on the stems and heads of grasses, reeds and sedges or, in respect of a few species, on crops where they can cause damage. Others though are scavengers feeding on micro-organisms, root aphids or on the eggs of spiders or grasshoppers.

As a result of their small size and difficulty in identification, the family are generally under-recorded. The most frequently observed species across the country are Oscinella frit and Elachiptera cornuta s.lat, both of which are in the Oscinellinae. Interestingly, that's not the situation locally as both of those species are some way down the pecking order. I live almost on the border of Dorset (VC9) and South Hampshire (VC11), so I always like to compare the latest distribution data from both areas and, in this case, Lasiochaeta pubescens sits clearly at the top of both lists, yet it's down in about fifteenth place nationally, which in itself shows that, regardless of habitat preferences, different regions will support different species. The problem though, is that unless you're in an area with active recorders, there simply aren't enough casual records to come up with a meaningful list of species that might be encountered. Saying that, I don't think it would be of much help here anyway, as virtually all chloropids require close examination to reliably determine the species.

The Chloropinae includes 76 species in 18 genera, the largest of which is Chlorops with 24 species and then Meromyza with 18. The most frequently recorded species are Cryptonerva flavitarsis, Thaumatomyia notata, and Chlorops hypostigma. The Chlorops species are mainly distinguished by having a bare frontal triangle and convex scutellum, and with the depth of the gena (jowls) being more than half that of the third antennal segment; the mesonotum is typically yellow with five black or reddish bands that are sometimes fused; the frontal triangle is coloured yellow to black, sometimes with ridges along the lateral margins; and the third antennal segment is generally deeper than long.

Identification to species is near impossible in most cases from photos, but the relatively common Chlorops pumilionis can be distinguished from other Chlorops, except C.adjuncta, C.speciosus and C.calceatus, by having a dusted sternopleural mark. Of course, there are other important features that need to be checked such as the broad ocellar triangle with a frontal central ridge, colour of the antennae, proportions of the gena etc., but looking carefully at a number of photos I took of the mating pair featured below, I think Chlorops pumilionis is a very likely candidate. They were found in the middle of a large area of grassland, which is the typical habitat of the species. The other tentatively named individual Chlorops hypostigma is a slightly smaller species with shining mesonotal stripes that are more noticeably separated before gradually tapering, a paler frontal triangle with a dark central mark and slender tarsi with only the lase segment darkened. Although this species may also be found in dry grassland areas, it seems to have a preference for damp woodland. In this habitat you could also find Chlorops gracilis or Chlorops specious, but they can be ruled out on appearance and probably time of year as I think that Chlorops hypostigma is the only one of the three that could be seen in October. The rather attractive, bright yellow, differently marked species that I photographed at Cashmoor Down are currently undetermined, so are simply shown as Chlorops sp.

Chlorops has similar colouration and banding of the mesonotum to Thaumatomyia, but there are consistent structural differences, notably in that the scutellum is convex with more widely positioned bristles in Chlorops, whereas in Thaumatomyia it's flat with closely-approximated apical bristles. Also, in Thaumatomyia the frontal triangle has one or more rows of marginal setae and the third antennal segment is more often than not longer than wide. Thaumatomyia is a much smaller genus with just five species, which makes identification possible. The most frequently recorded is Thaumatomyia notata as previously mentioned, then glabra, hallandica, trifasciata and finally rufa, which can probably be ignored as it has very few confirmed observations.

In respect of the individuals photographed at Martin Down, the key feature is the greater width of the gena, deeper than the third antennal segment, which immediately rules out the common Thaumatomyia notata. The scutellum has more than twenty bristles so it can't be Thaumatomyia glabra and the frontal triangle is shiny. It also has more of a yellow- brown, rather than bright yellow, background colour. This all keys out to Thaumatomyia hallandica, a species that is found both on coastal sand-dunes, but also inland on dry sandy grassland, sandy heaths and chalk downlands. Thaumatomyia trifasciata has an even deeper gena, which is 1.5 to 2 times as wide as the third antennal segment is deep, and is a species that would not be found in this habitat as it primarily seems to occur in marshes and around pond margins. Thaumatomyia notata is a tiny species, highly variable in colour where the frontal triangle and abdomen may be yellow or black and, consequently, best identified by the very narrow gena. It can be found in a range of habitats from open areas of woodland to gardens, where it is most abundant on the foliage of low bushes and shrubs particularly early and late in the year.

The Oscinellinae is the larger of the two subfamilies with just about a hundred species, which are generally small flies with dark colouration. The various genera have certain features that enable them to be separated into groups to aid identification, but they require proper examination and, consequently, a genus is about as good as it's likely to get from photos. However, with many individuals you probably won't even get that far, although the first photo featured below captioned Lasiambia sp. was identified by an expert on the UK Diptera FB group and likely Lasiambia palposa s.lat or possibly Lasiambia brevibucca, but impossible to be sure. Similarly with the other individual that I photographed in the garden although, with that one, even the genus is a tentative suggestion.

Footnote:

Whilst I've tried to be careful with my descriptions, please remember that I'm looking at this family purely from a photographer’s perspective in order to have a basic level of understanding so that I can have a go at tentatively naming some of the different species I've encountered.

Revised, Dec.24 (v.3)