The mystery of Britain's disappearing butterflies

Did you notice the butterflies going? Look around you: in many of the above places, where you see nothing, your parents would have seen butterflies. If you are over 40, you may have a hazy feeling that there seemed to be a lot more small tortoiseshells and meadow browns and "cabbage whites" about when you were a child, and you would be right.

Of course, there are still butterflies, especially on warm summer days, and in some places, still in substantial numbers. But one of the most meticulously recorded sets of wildlife data put together has shown convincingly that in the past 25 years, seven out of 10 of Britain's butterfly species have declined, some by amounts so large they are on the road to extinction.

Widespread and formerly common species such as the grayling and the wall brown have dropped in numbers by 40 per cent and more, and vanished from large areas, and others, including the pearl-bordered and high brown fritillaries, have suffered catastrophic losses (half the colonies of the pearl-bordered fritillary have gone in 10 years).

The tiny but resplendent small copper, the spectacular purple emperor, the glowing Adonis blue, even the large and small whites, long the bane of gardeners for their caterpillars' love of cabbage leaves, are all on a steadily downward trend.

Yet this astonishing fact, that more that 70 per cent of British species are declining, that Britain is steadily losing its butterflies, has not yet entered the public mind. So a week today, the man who is leading the fight to save them, Martin Warren, chief executive of the charity Butterfly Conservation, is beginning a sponsored walk along the coast of southern England to try to draw it to people's attention, handing out leaflets headlined, Don't let butterflies become dinosaurs of the future.

Dr Warren said: "We knew numbers were going down; there are far fewer places now where you can walk through a field and put up thousands of butterflies. But when the true extent of the decline emerged, we were genuinely shocked."

This was disclosed last year when a group of British conservation scientists did an in-depth statistical comparison of two atlases of Britain's butterflies, one published in 1984 and the other in 2001, and each containing thousands of observations.

The team, led by Dr Jeremy Thomas, Britain's leading butterfly expert, also did similar comparisons with atlases of British birds and wild flowers, and found that 28 per cent of native plant species had decreased, as had 54 per cent of bird species, and 71 per cent of butterfly species were on the way down.

In a world of increasing wildlife loss, they are the group of organisms falling fastest. The main cause is largely that which has caused the declines of flowers and birds: loss of the special places each species needs to breed, because of intensive farming practices and development. But there are three reasons in particular why butterflies are showing such losses.

First, their annual life cycle of egg, caterpillar, chrysalis and adult insect is delicately poised and can be easily disturbed, so they respond to change very quickly: they can be gone in a year. Second, they often need active management of the landscape. Woodland butterflies need sunny rides in which to breed, and if the rides become overgrown they will die out.

Third, some butterflies need large areas in which to flourish, because they are subject to population crashes, often caused by parasites, and small isolated populations which have no chance of being renewed are likely to go extinct.

To show us what Britain's butterflies used to be like and still could be like, Dr Warren took The Independent at the weekend to Bentley Wood, a large broad-leaved woodland near Salisbury in Wiltshire, owned and run by a charitable trust with conservation as a prime aim.

With the warden, David Lambert, who manages the wood for butterflies, we saw a spectacular succession of 15 species in two hours; the highlights included white admirals feeding on bramble flowers, dozens of breathtakingly lovely silver-washed fritillaries and fleeting glimpses of what attracts many visitors to the wood, the purple emperor.

Britain's most majestic butterfly declined to come down and pose for us, but we met excited visitors who had had just that experience; they eagerly showed us their photographs.

It was clear what butterflies meant to them. But in truth you would have to have a particularly stony heart not to respond to these insects, not to love them for their vibrant splash of colour and their signalling of the seasons. Who doesn't feel gladdened by the first red admiral?

In Britain, we have only 57 resident species and three common migrants, and France has more than 300. But they add enormously to the pleasure of the countryside. Dr Warren's walk next week is to warn people that such pleasures can no longer be taken for granted.

* Martin Warren's sponsored walk is along the South Coast Path from Exmouth in Devon to Swanage in Dorset from Monday 25 July to Sunday 31 July. It can be sponsored (or just followed) on the Butterfly Conservation website, www.butterfly-conservation.org.