Just how fragmented and isolated are some of the populations of Britain's butterflies is brought home to you when you try to see them all in a single summer, as I did last year as part of The Independent's Great British Butterfly Hunt. I managed to see all the five declining species about which conservationists are now so concerned, but to do so meant travelling from end to end of the land. It wasn't that I wanted to. I had to. To find these creatures which once were familiar throughout the countryside, you have to go a long way nowadays.
I started with the Duke of Burgundy, the titchy but charming rarity which is vanishing at a rate of knots, and I glimpsed it on May Day on the top of Butser Hill near Portsmouth, one of the highest points of the South Downs – once the sea mist cleared and the sun came out. And I saw the pearl-bordered fritillary on 25 May in Bentley Wood in Hampshire, which is increasingly recognised as one of the best sites for woodland butterflies in all of Britain. They weren't that bad in terms of travel from London, these outings. About 80 miles in each case. Still, it took a full day to do them.
But to see the splendid but very rare high brown fritillary, I had to get on the Glasgow train on 28 June and rattle up 300 miles to Arnside Knott in Cumbria, the lovely limestone hill which looks across to the Lake District, and stay overnight; and to catch a sighting of the bee-like Lulworth skipper I had to get on another train on 23 July and head to Lulworth Cove in the chalk cliffs of Dorset's Jurassic Coast.
Only the floppy, delicate wood white was within reasonable distance of home – I saw it in Chiddingfold Forest, Surrey, on 29 July.
The point is, these creatures are now scattered across Britain in tiny groups and increasingly vulnerable to local extinctions. In each case, just glimpsing one in the wild feels like a significant achievement.
It is a far cry from the clouds of butterflies of which Victorian collectors used to speak, and which can only be infallibly seen now in places like the Picos de Europa in Spain or the Cévennes in France (although , bizarrely, one place you still might see that in Britain is at Porton Down, the chemical warfare establishment in Wiltshire).
The presence of butterflies such as these is a strong indicator of the health of the surrounding environment. Increasingly, what we are finding is their absence. Draw your own conclusions.