On a bright spring day, the chalky slopes of the Chiltern Hills in southwest England smell of warm thyme. Tiny purple violets bloom underfoot. For miles beyond, the Vale of Aylesbury unfolds in a tapestry of newly minted trees, yellow fields and the spires of village churches. This great vista of the English countryside seems gloriously immutable, unchanged since Victorian times, when Walter Rothschild would set out from Tring Park, his country house in the valley below, to throw his net at our summer butterflies and place them in his extraordinary zoological museum.
Not everything, however, would please the eye of Victorian lovers of nature. An easyJet plane casts a shadow across the downland. The air is filled with the complaint of two diggers, quarrying chalk from the bottom of the hill. But what would really make Rothschild weep is what is missing: The sky and the steep meadows dotted with the white flowers of wild strawberry are almost bereft of butterflies.
A casual eye might not notice it. Butterflies are still a conspicuous symbol of our summers, much celebrated by everyone from Wordsworth to Nabokov. On the Chilterns, a male orange tip patrols a hedgerow, two peacocks spiral into the air in a territorial dogfight and a speckled wood jinks its way through the trees. This scattering of a few common species is pitiful, however, compared with the riches that once adorned our countryside in summer. Near contemporaries of Rothschild wrote of skimming hundreds of purple hairstreaks from the trees or catching 100 Lulworth skippers in an hour. In 1892, SG Castle Russell took a walk through the New Forest, south of the Chilterns: ?utterflies alarmed by my approach arose in immense numbers to take refuge in the trees above. They were so thick that I could hardly see ahead and indeed resembled a fall of brown leaves.?br />
A few centuries earlier, Richard Turpyn recorded a probable mass migration to or from Britain in his Chronicles of Calais during the reigns of Henry VII and VIII: ?n innumerable swarme of whit buttarflyes ... so thicke as flakes of snowe?that they blotted out views of Calais for workers in fields beyond the town.
Swarms of butterflies have long disappeared. And a relentless decline may now become terminal for some of our best-loved species. Following the wet summer of 2007, last year was a disaster for butterflies: The lowest number was recorded for 27 years. Of Britain? precious 59 resident species, 12 experienced their worst ever year since the scientific monitoring of butterfly numbers began in 1976.
I began a less than scientific monitoring of butterflies in a little notepad when I was eight, helping my dad count the tiny brown argus on the Norfolk coast, eastern England, where we spent our summer holidays. Finding this darting, chocolate-brown gem ignited an awkward passion for butterflies that I kept well hidden during my teenage years. Dad and I would go on expeditions to discover, and photograph, rare species: We would sit in a wet meadow in Cumbria, northwest England, waiting for the marsh fritillary to emerge, or hover by piles of horse manure in the woodlands of Surrey, outside London, hoping the majestic, haughty (and turd-loving) purple emperor would descend from the treetops for us. Twenty years on, some of the nature reserves we visited have lost their precious rarities. If trends continue, another couple of bad summers could kill off some species for ever.