Ephydridae

Shore Flies (1)

DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > SCHIZOPHORA > Acalyptratae > Ephydroidea > Ephydridae (153 species)

(subfamilies: Discomyzinae, Ephydrinae, Gymnomyzinae, Hydrellinae and Ilytheinae)

A large family of tiny to medium-sized (1-10mm) mainly dark-coloured flies that inhabit a variety of aquatic or semiaquatic habitats. The common name of the family may suggest that these species are primarily found on the seashore but, in fact, the vast majority of British ephydrids are actually freshwater flies that occur inland, living in marshy wetland areas or on the muddy banks of ditches, streams, ponds or even larger bodies of water.

The 150+ British species are placed within 40 or so genera in various tribes that are then separated into five subfamilies; the largest being Hydrellinae and then Ephydrinae with 50 and 44 species respectively. The largest genus is Hydrellia with 29 species.

The different species are rather variable in form, which make the family as a whole difficult to characterise in general terms, although with some there's a feature that stands out, quite literally, in that they often have a rather distorted, somewhat swollen face that gives them a toad-like expression.

Although some ephydrids are generalists, most species are associated with a particular type of habitat, which is always a useful indicator when trying to identify individuals and also a convenient way to break down large families. In this case, we can broadly split them into two groups, the freshwater /wetland flies discussed here and the species that inhabit coastal / saltmarsh areas which are featured on the next page.

A quick look at the currently available distribution data on the NBN Atlas shows that they are a largely neglected and poorly recorded group of species, despite being common and widespread in many areas. In Dorset (VC9) and South Hampshire (VC11) combined, there are less than 150 confirmed sightings. The most frequently recorded species locally are Parydra coarctata, Hydrellia maura, Psilopa nitidula, Hydrellia griseola and Scatella lacustris and, not far behind, Ochthera mantis and then a number of Notiphila species.

There are actually 16 described Notiphila although, as far as I can deduce, only seven are likely to be seen locally. They are medium-sized, 3-6mm body length, flies with a generally greyish or brownish colouration, distinguished from other genera by having no hairs around the mouth margin and, apart from the sides, most of the face bare; costal vein ending at R4+5; two pairs of dorsocentral bristles; and the dorsal surface of the middle tibia with a few erect bristles. In most cases they cannot be reliably identified from photos and are best left as Notiphila sp., but there are certain features, especially the colour of the antennal segments and the extent and definition of any markings on the thorax or abdomen, that may provide clues to a likely species. For example, Notiphila riparia has yellow antennae with a darkened third segment coupled with a general greyish colouration, an almost uniformly coloured mesonotum and tergites with markings that are more distinctly differentiated from the paler areas than seen in many of the other species. Notiphila cinerea on the other hand, which has a more brownish-grey colouration, has an indistinct abdominal pattern where the margins of the darker patches tend to merge more gradually into the paler areas. It also has antennae with a dark blackened second segment that extends partially onto the third before turning yellow. Notiphila venusta has a similarly coloured antennae, but can be distinguished to some degree by having three narrow dark stripes on the scutum. Notiphila maculata also has markings on the thorax but, they are more distinct, appearing as dark brown interrupted streaks that run along the lines of the setae. The three remaining species that need to be considered are Notiphila nigricornis that has entirely black antennae, Notiphila graecula which is rather similar to Notiphila cinerea and Notiphila dorsata which has a more brownish colouration and a bold abdominal pattern. Obviously, there are a number of other features that need to be checked but, at the very least, the general colouration and markings help separate the species. And, of course, it's quite likely that most of the individuals seen at a particular location are probably the same species.

Notiphila (subgenus Dichaeta) caudata is a relatively large, dark, almost entirely brownish-black species with several narrow paler lines on the mesonotum, vein R2+3 with a distinct bend midway along, and conspicuously stout facial setae that are much the same length as the bristles on the body, which gives it a distinctive appearance. After having the individual I photographed at Janesmoor Pond confirmed, I checked the NBN Atlas and discovered that this species had only been recorded once in Dorset, and only once before in South Hampshire, which was also in the New Forest, but way back in 1952.

Ochthera mantis is unmistakeable due to the greatly enlarged front femora. Although three Ochthera species are listed, one is almost certainly extinct and the other Ochthera manicata is extremely rare outside of a few areas in East Anglia. Unfortunately, I only have one photo of this particular fly as, despite being easily distinguishable, I didn't appreciate at the time that it was a different species.

The previous species I've mentioned were all found as individuals, whereas my photos of Parydra coarctata show that there were quite a number feeding together. They were all settled on and around a muddy patch of ground on a track through a wetland area that regularly becomes waterlogged. I managed to determine the correct genus, but not the species. Fortunately though, the photos showed enough detail for an ephydrid expert on the Diptera UK FB group to positively identify them from the lack of a large bristle on the mid coxa and the presence of an apical tubercle on the scutellum, which are two important characters of this species.

Although Parydra coarctata is the most frequently observed ephydrid species from both Dorset and South Hampshire, there are nine further species in this genus, with Parydra fossarum, Parydra hecate, Parydra littoralis and Parydra quadripunctata all having been recorded locally at some point. Determining the actual species may be tricky, but fortunately Parydra littoralis can be visually identified by the mid tibiae being anterodorsally shining black with silver- dusted patches at the base, middle fifth and tip which, from the right angle, show up nicely (almost as though the legs are banded) making it easily recognisable.