DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > SCHIZOPHORA > Acalypratae > Diopsoidea > Psilidae (28 species)

(subfamilies: Chylizinae and Psilinae)

The Psilidae family - the common name coming from the general colouration of the narrow-bodied Loxocerini species -consists of small to medium-sized (3-10mm) slender to stout flies with a yellow to reddish, brown or black body with relatively few bristles; a head that is circular or somewhat angular in profile with a projecting frons, eyes of very variable size, antennae that can be small or with the third segment conspicuously elongate, arista short or longer and pubescent, ocelli present within a large ocellar triangle; wings that are usually clear although sometimes yellowish or smoky, the costa with a distinct break some distance back from the end of vein R1, the end of vein Sc turning almost vertically upwards into this costal break as a hyaline or whitish streak on the wing surface, second basal and anal cell long and wide, cross-vein BM-Cu present, and cell cup closed; the tibiae are without dorsal preapical bristles. 

The larvae are mainly phytophagous feeding in the roots and stems of a wide range of plants.

There are twenty-eight recognised species on the current British List separated into two subfamilies; Chylizinae with 5 species in the genus Chyliza; and Psilinae, which is split into two tribes, Loxocerini with 5 species now in two genera, Imantimyia (4) and Loxocera (1), and Psilini with 18 species in three genera, Chamaepsila (15), Psila (2) and Psilosoma (1)

Although I don't expect to photograph many of these flies, it's always good to have knowledge of the taxonomic arrangement for when a genus, or hopefully a species, is being considered. It's also useful to check the NBN Atlas for local sightings. Obviously, it can only show information from submitted and confirmed records but, regardless of how true or current they are, the data provides a good insight into what species are likely to be seen.

In this respect, I can clearly see that Imantimyia albiseta and Psila fimetaria are by far the most frequently recorded. In fact, the combined records from both Dorset (VC9) and South Hampshire (VC11) show that these two species alone account for more than twice the number of all reported psilids. However, it also needs to be noted that this is actually a poorly represented family particularly over the past few years as most of the records are quite old.

With regard to identification, members of the Psilinae subfamily can pretty much be differentiated from the Chyliza species by the shape of the face when viewed in profile, being angular and strongly retreating with the side margin of the mouth opening forming a continuation of the facial curve, whereas in the Chylizinae it is concave.

The six species of the Loxocerini tribe can be distinguished by their long antennae, specifically the third segment which is four times the length of the second and much longer than the face, whereas all of the species within the Psilinitribe have much shorter antennae. Loxocera aristata is a possible species locally. It's one of the larger species (7-10mm) with a black face, reddish median frontal triangle with dull black markings each side, and a third antennal segment that is only a little longer than the arista. Imantimyia albiseta is a tad smaller (> 9mm) with longer antennae, a frons that is usually narrowly and vaguely yellow along the eye margin, the occiput (back of the head) and the humeri (anterior corners of the thoracic dorsum) darkened, and the scutellum brownish-orange; this final feature helps to separate it from the rare New Forest species Imantimyia nigrifrons, which has an all-black frons and scutellum. If unsure, the other two Imantimyia species should be considered, but they are extremely unlikely in my area; Imantimyia sylvatica with yellow humeri and scutellum, and Imantimyia fulviventris with darkened humeri and scutellum.    

The Psila genus is largely distinguished by having no postvertical or orbital bristles and only two outer and two inner verticals, whereas the Chamaepsila species always have a pair of postverticals however small. Whilst Psila merdariacould possibly be encountered in Hampshire, it's an unlikely species in Dorset as it doesn't appear to have spread this far west. Psila fimetaria on the other hand is the most observed species in the county. It has a couple of important distinguishing features that should be visible in photos. Firstly, the third antennal segment is distinctly darkened on its outer side at the base of the arista. The other is that the scutellum is slightly shorter in proportion to its width - longer in Psila merdaria - and the pair of strong bristles at the rear are well spaced. 

There are two further species that need to be mentioned;Chamaepsila rosae (formally Psila rosae) the well-known agricultural pest, commonly called the Carrot Fly. It doesn't have many records, but it must be present in certain areas; the other is Chyliza leptogaster, historically well recorded in Dorset, except the last record was back in 2006.

July 24