Common Darters (Sympetrum striolatum) egg-laying - which this species do 'in tandem' as seen here. The male retains his grip on the back of the female's head after mating, and they both go off and find somwhere to lay the eggs - she dips her tail in the water, repeatedly, dropping off one egg each time. I often try to photograph this behaviour, but almost never succeed. Today was one of the almost nevers.