Williamson's Weekly Nature Notes October 1 2008

Amazing to find this once-common insect vanishing from our countryside.

Everybody has noticed this. But wait: not so fast. This gorgeous cottage garden denizen, of those long warm summers and autumns of our youth, is actually up to its usual tricks again. I spy with my little eye a graph in a Defra report. It bounces up and down like a golf ball on concrete. It belongs to the small tortoiseshell.

It starts in 1976 and bounces along for 31 years. It is the weekly count for three decades by 3,200 recorders, mostly volunteers, of just one of the UK's 56 species of butterflies. I have been one of them for 31 years; my wife, Anne, another for 28 years.

Each week in the season of 26 weeks we record what we see over exactly the same walk on the finest day of the week. My walk is five miles; hers is a mile and a half.

Butterfly counters cover 1,453 areas of butterfly country. Defra leads the consortium of a dozen countryside agencies that aims to follow the fortunes of our most popular and pretty insects.

The results tell us what is happening to them '“ what farming is doing to them, also pollution, climate change, development, management of nature reserves: the lot.

There is a bouncing graph for every butterfly. Some bounce a little like the Dambusters' bomb. Some go mad like a golf ball. The maddest one of all is that of the clouded yellow.

Millions sometimes swarm into Britain. The next year: hardly one. The steadiest is the orange tip. Some, like the silver-studded skipper, bounce a bit but are steadily climbing all the while. They have doubled their number in 30 years. Some, like the white-letter hairstreak, are slowly declining. Understandable, because their caterpillar feed on elms. Most are following a steady line overall.

Our small tortoiseshell is on one of its periodic seven-year lows. The last one was in 1999. It should now climb back to another high in 2012.

All these swings are natural. And it may be that they are superimposed on much larger swings that might be a century from peak to peak and trough to trough. But we won't really know that for another 100 years I imagine. By which time, at the present rate, I shall have walked a total of 12,000 miles and counted 700,000 butterflies.