August - The Summer Dun

Siphlonurus lacustris 

The summer dun is a widespread (see coloured area on map below), though uncommon species.  The nymphs typically live in the pools and margins of rivers and streams, lakes and in pools at high altitude.  The large nymphs are good swimmers and typically swim in short, darting bursts.
 
Emergence of the adults typically takes place partially or entirely out of the water on a stick, stone or plant stem during daylight hours.  Males of this species swarm throughout the day.  Once mated, the female flies upstream and descends to the surface of the water releasing a few eggs by dipping the tip of her abdomen into the water at intervals whilst flying over, or by actually settling on the water surface for short periods.
 
There is one generation a year, which overwinters as eggs.  Adults emerge between May and September, although the main flight period is from June to early August.

Craig Macadam
 



The Summer Dun dun/subimago Copyright Cyril Bennett

 


Courtesy Ephemeroptera Recording Scheme