Arthroplea congener Bengtsson, 1909

Nymphs: Flattened nymphs with broad heads.  The eyes are large and placed on the back of the head.  Long brush-like structures (maxillary palps) extend forward from the head.

Adults: Medium sized flies with two tails and large hindwings.  The body is dark brown, almost black with each segment slightly paler on the sides and rear edge.  Segments 2 to 8 have two dots on either side of the mid-line.  The wings are slightly opaque, particularly in the lower half.  The legs are brown to dark brown and the foot is much paler.  The tails are a smoky grey colour with rings at the joint of each segment, particularly in the segments closer to the body.

Nymphs: Arthroplea congener has distinctive maxillary palps (a), which make it unmistakeable for any other species.

Adults: The separation of Arthroplea congener from other Heptageniidae relies upon the features found in male imagines.  It is recommended that a specialist key is used if you suspect that you may have a specimen of A. congener.

Nymphs of this species live chiefly in the pools and margins of rivers and streams, where they cling to submerged plants and stones, although they may swim if disturbed.  They feed by filtering of gathering fine particulate organic detritus from the sediment.  There is one generation a year, which usually overwinters as eggs and emerges between May and June.

Arthroplea congener no longer occurs in the British Isles.  The only record is of a single adult male taken in 1920 at Stanmore, Middlesex.  As a result, a voucher specimen is required for all records of this species.