A thing of beauty is a joy forever?Sadly not so for the adult mayfly whose exquisite ephemeral beauty lasts for just a few hours or at most a day.

Britain has forty six species of mayfly of which danica,the largest,is by far the most stunning with bright shimmering black-veined upright forewings,hooped ochre coloured abdomen,three filamental tails and forward pointing front legs(see picture).

I'm sitting by the Thames at Richmond watching many danica lifting from the surface with weak fluttering flight.Having spent two years as a nymph on the river bed feeding on detritus,the aim of the emerging mayfly,at this stage called a dun or sub-imago is to reach the river bank.But,swifts and wagtails have spotted the insects and fly fast and low scooping them up.

Mayflies that do make it to the bank perch on vegetation,rest a while and then undergo their final moult to become imagos or perfect insects.Delicate perfection they certainly are,much admired by me and relished by trout.

From late afternoon adults join a mating swarm by the riverside wafting vertically up a metre or so,then parachuting down,up,down in rythum until pheromones dispersing,pairing takes place in mid-air.

Mating complete,males die,leaving females to perform their final act of egg laying on the water.That done,their wings collapse onto the surface,a brief struggle ensues then exhausted,they also die, many to be eaten by fish.So brief is the life of a mayfly that its mouthparts are useless as they have no need to feed as an adult.

Anglers call the mayfly season 'duffers fortnight'implying that any novice fisherman will catch trout as they indulge in a mayfly feeding frenzy.