`He lies at the watch for any fly or minnow that comes near to him; and he especially loves the May-fly, which is bred of the cod-worm, or caddis"
Izaak Walton's The Compleat Angler was published in 1653. It combined practical information for the rod fisherman with snatches of mythology and folklore, and quotations from classical writers as diverse as Pliny and du Bartas. Walton drew an idyllic picture of a rural life and well-kept inns, with pastoral interludes of song and verse and homely entertainment.
But there is more to the mayfly than Walton or his classical advisers thought. The mayfly nymph spends a year or two buried in the mud or sand at the bottom of a stream or pond.
From there it emerges into the open air, with millions of its fellows, in an annual event we call the "rise". It undergoes a series of metamorphoses to become an adult, an insect about two inches long with semi-transparent lemon-coloured wings.
Adult mayflies have a brief, pleasurable existence: their energies are exclusively devoted to mating. This they do in dense and feverish swarms, the objective in the case of any individual often being achieved within an hour or two. Almost immediately the female deposits eggs into the river or pond, and very shortly afterwards she and her recent paramour collapse exhausted on the surface of the water, there, with wings outstretched, to expire in a classic denouement unequalled even in Tchaikovsky's ballets.
This brief sojourn en masse above the water takes place dramatically each spring - indeed as the insect's name implies, very often in the month of May.
It is known that mild dry sunny weather brings an early "rise", but the reason why has proved elusive. It may be because the water temperature is high. Alternatively, it may depend on the amount of sunshine, which heats the silt of the shallow waters where the larvae grow. The sunshine may help the growth of algae which provide the food, and bring about an early hatch. Or it may be rain-related, since low rainfall means lower water levels, leaving the water rich in nourishment.
Whatever the reason, the annual "rise" of the mayfly provides a tasty morsel for many a waiting trout. The abundance, as Walton says, makes the fish "more bold and lusty" than they normally are, providing a bonanza for the angler casting with his rod.