This is a female mayfly carrying a green egg sac. It is a small to medium-sized mayfly with a reddish-brown body, three tails, and large hindwings. Similar to Leptophlebia marginata, which has a dark smokey wingtip. Length 11mm.
The nymphs are poor swimmers so move amongst dense aquatic vegetation. They feed on fine organic detriment from the sediment. The females lay their eggs by dipping the tips of their abdomens on the surface of the water, and each individual can lay up to 1200 eggs. Once the female has done laying her eggs she dies and falls on the surface of the water.
It flies April to August, and the nymphs and adults of this species live in and around the margins of slow-moving streams, ponds and lakes, mainly in acidic regions. Fairly common throughout Great Britain and Ireland.
Photographs taken July 2013, rear garden, Staffordshire.