To be at the riverside during a mass emergence of mayflies is to witness one of the most enthralling events of the natural world. Of exquisite beauty, adult mayflies live for just a day, or even seconds if unlucky.

Mayflies are large up-winged insects beloved of fishermen and predators alike. (pictured)  Living as nymphs on the river bed for two years feeding on detritus, they float to the surface in May and June to complete their life-cycles.

Once at the surface wings rapidly dry and they lift off with weak fluttering flight heading for bankside vegetation. At this stage they are called duns. Safely perched, they then undergo a final moult to become imagos, ready to join an evening mating flight. Such flights number hundreds of individuals  bobbing up and down to couple in mid-air. Mating completed, males die leaving females, now known as spinners to fly back to the river to lay eggs  on or just under the surface before they too become exhausted and spread- eagled, expire.

Over one hundred and thirty million years of evolution mayflies have lost use of mouthparts and stomachs for with only hours to live  they have no need to feed.

On  the Thames at Kingston on a sunny breezy May afternoon clouds of mayflies wafted over the towpath. They were the fortunate ones. Swifts and swallows scooped  many off the surface or in mid-air while starlings and wagtails risked a ducking by hovering above the river to grasp hatching mayflies before they had a chance to fly. Great crested grebes also joined in to make the most of the rich bounty.

Such miniature perfection but such transience.