One fine morning at the end of the spring I did a butterfly walk, but not a casual butterfly walk. I counted what I saw, which included 35 dingy skippers, 28 common blues, eight grizzled skippers, six brown arguses, five brimstones and singles each of the small tortoiseshell, the large white, the small heath and possibly of great rarity, the Duke of Burgundy (which flew past very quickly).
It was a walk of real delight, because while the two little skippers are indeed somewhat on the dingy or the grizzled side, they are by no means common butterflies in most of Britain and encountering them is a pleasure, while the common blue is a truly lovely creature, as is its cousin the brown argus—this last a brown member of the blue family, its dark wings bordered with brilliant orange spots.
I didn’t have to go far to find them. Our village sits between two steep chalk downland hills, both of which are wonderful butterfly sites, each holding more than 30 different species; but while one is famous for its spectacular ancient monument and often dotted with tourists, the other, which is harder to find your way onto, is empty for most of the time. So I gave The Famous Hill a miss and chose The Other Hill for my expedition, which was with Bernard Franklin from the Dorset branch of Butterfly Conservation, because he was showing me how to walk a butterfly transect.
One of the sad wildlife truths that has dawned on us in recent years is that insect populations are tumbling in many parts of the world. In Britain about seventy per cent of our 58 butterfly species are declining either in their abundance or in their range, probably because of the intensification of farming, although in some cases climate change may be starting to have an effect. But here’s a question which may interest you: how do we know?
I mean, we can’t go out and count all the butterflies in the land, can we? How many red admirals will there be flying around in Britain this year? Ten thousand? Fifty thousand? A million? You can’t count ‘em all. And anecdotal evidence is no good—as in, ‘I don’t seem to see as many red admirals as I used to.’ Maybe you’re just not looking hard enough, or you’re not looking in the right places.
The way to get a proper scientific idea of what is happening to insect populations is by sampling them, and then comparing the samples year by year. And a particularly clever way of doing this has been devised for butterflies: the transect. This is a weekly walk done in good weather throughout the summer months, following exactly the same route in exactly the same place, and recording every butterfly seen within a five-metre ‘box’ around the observer. These standardised counts produce figures which are statistically robust; they have been taking place every year since 1976 and more than 2,000 are now walked every week across Britain, with the data fed into the UK Butterfly Monitoring Scheme, so now we have a pretty good idea of how our butterflies are faring nationally. (And 22 other countries across Europe have taken up the idea.)
But walking a butterfly transect, as I did with Bernard along the base of The Other Hill and then back along the top, is not just a valuable piece of citizen science; it is immensely enjoyable, not least for the changes in species throughout the season: by the time you read this the browns will be on the wing there, the meadow brown, the gatekeeper, the ringlet and the marbled white (which is a white member of the brown family). And enjoyable too for the lovely wildflowers—the horseshoe vetch, the rock rose, the bird’s foot trefoil and the thousands of tiny lollipops sticking out of the grass which are the flower heads of salad burnet. And for the views of the village, which are sensational. But mostly for the butterflies.
