Mayday for mayflies, manna from heaven

'For miles, the surface of the river was white with mayflies as they hung over it on gauzy wings'

Last week I went to visit Kelmscott Manor, which isn't a fishery but was the holiday home of the founder of the Arts and Crafts movement and his wife and their friend, the painter Dante Gabriel Rossetti. It sits just on the banks of the Thames (although it's known as the Isis in them there parts).

Last week I went to visit Kelmscott Manor, which isn't a fishery but was the holiday home of the founder of the Arts and Crafts movement and his wife and their friend, the painter Dante Gabriel Rossetti. It sits just on the banks of the Thames (although it's known as the Isis in them there parts).

The mayflies were out and what a beautiful sight they were, flying up and down in a straight line. Almost like pole dancing. I was with my friend Valerie, a New Yorker, who once called out Rentokil to liberate a squirrel stuck in her bedroom ("£160 well spent"), and who makes high-pitched "help me" phone calls to friends, when there's a "fuzzy bee" trapped in her house.

"Urgh! Look at those bugs," she shuddered as we went through a biblical swarm of them. I tried to tell Valerie the story of the mayfly and hopefully instil some love in her for these magnificent creatures - "See them dancing now, they're at the disco, looking for a mate"- but to little effect. When I told her they only lived 24 hours after a two-year gestation, she said, "That's the best thing I've heard about them so far".

Mayflies mark the start of spring for me and certainly the start of some bloody good fishing. Seeing them in such large numbers is privilege indeed. Entire generations of mayflies have been wiped out in some rivers due to pollution. It's more common to see big groups of them in warmer climates. There have been tales (going back some years now) of "swarms of incalculable numbers so as even to weigh down the shrubbery upon which they rest". In the late 19th century, fishermen in France actually thought the mayflies descended from heaven (bless 'em), and called the "living cloud" manna.

This was as nothing to a 1895 description of the mayfly hatch on a river in New Guinea: "For miles, the surface of the river, from side to side, was white with them as they hung over it on gauzy wings; at certain moments, as if obeying some mysterious signal, they would rise in the air and then sink down anew like a fall of snow." A hundred years before that, records show they were so abundant in certain parts of the world, the dead mayflies "were gathered by the cartload and used as fertiliser".

Insects are very delicate little creatures; an act of pollution that may not affect fish or fowl can wipe them out. But if the layman doesn't notice the decline of fish until it's on TV, he notices the decimation of insects less. But when there are no insects to feed upon, fish numbers invariably decline too. We now have a quarter of the fly population we did in the 1930s, and in just the last two years it has declined by a third. We only have 40 per cent of the mayflies we had before the Second World War, which actually seems like a lot when you compare it to a fly called the Iron Blue, whose numbers are down by 80 per cent. Reasons for this decline include the aforementioned pollution, climate changes, changes to the way farming is conducted and water abstraction. All impact on the ecosystem of rivers.

Last year, a colony of mayflies was lovingly hand-reared by a freshwater biologist, Cyril Bennett. Eggs from the Test in Hampshire were gathered and put into the south Wey in Surrey, to try to restore the community of invertebrates to that river. But someone, somewhere, in an act of staggering ignorance and laziness, poured some household or garden insecticide down the drain to get rid of it. And a million mayflies were wiped out.

It wasn't concentrated enough to kill the fish, but the mayflies and other invertebrates in the river were just too delicate to withstand it and perished.

Mayflies date from the Jurassic period at least. They've outlived dinosaurs, I wonder if they'll outlive us.

a.barbieri@independent.co.uk