Leptophlebia marginata (Linnaeus), 1767

Nymphs: Streamlined nymphs with branched gills.  Tails are as long, or longer than the body and held in a 'T' shape at rest. 

Adults: Small to medium sized flies with three tails and large hind wings.  The sub-imago of Leptophlebia marginata has pale fawn, heavily veined wings and an overall dark brown appearance.  On closer examination, the body can be seen to be rich, dark sepia colour.  Both the male and the female imago have reddish brown bodies however in the male the body segments are ringed with a straw colour.  In both sexes the wings have pale brown veins, however the female imago has smoky black patches along the leading edges of the forewings.

Nymphs: Leptophlebia marginata can be separated from L. vespertina by the coverage of teeth on the claws and by the shape of the gills which gradually taper from the gill plate to the tip of the gill.  L. marginata is the largest of the two Leptophlebia species found in the British Isles.

Adults: The British Leptophlebia species can be separated by colour and venation of the wings.  In L. marginata the forewings of the sub-imago are brownish grey and the veins are marked out in a brownish colour.  The hind wings are of a similar shade to the fore wings.  In Leptophlebia vespertina the fore wings of the sub-imago are pale grey and the hind wings are noticeably paler than the fore wings. 

Imagines of L. marginata have brownish forewings, particularly at the wing tip and the veins are brown, tending towards yellow.  The wings of L. vespertina imagines are clear with pale brown veins.  There are no appreciable differences in the shade of the hind wings in the imago of either species.

Nymphs of this species can be found in the pools and margins of slow flowing streams and in ponds and lakes where they climb upon the surface of leaves of aquatic plants or crawl in the surface layers of fine sediments, especially mud.  The nymphs are poor swimmers but are adapted for moving amongst dense stands of plants, especially on the surface of the stems.  They feed by gathering fine particulate organic detritus from the sediment.  There is one generation a year, which usually overwinters as nymphs and emerges between April and June.

Nymphs are seldom found in the shallower margins of lakes in any quantity until early April.  As the period of peak emergence approaches, many of the nymphs move into very shallow water.  Emergence of the adults takes place during daylight hours at the surface of the water or more typically, partially or entirely out of the water on a stick, stone or plant stem.  The males of this species can be found swarming throughout the day. 

Once mated, the female flies to the water to release a few eggs by dipping the tip of her abdomen on to the surface at intervals, or by actually settling on the surface for short periods.  After several visits to the water her supply of around 1200 eggs is finished and the spent female falls on to the surface.

Leptophlebia marginata is a fairly common species that has been found throughout the British Isles, including Ireland.  It is particularly tolerant of the effects of acidification and has been found in waters with pH values of between 4 and 5.