Free Field Notes From a Catastrophe: Man, Nature, and Climate Change by Elizabeth Kolbert

every city, and many a small town, supported its own entomological society. In the 1970s, Britain’s Biological Records Centre decided to marshal this enthusiasm for a project called the Lepidoptera Distribution Maps Scheme, whose aim was to chart precisely where each of the country’s fifty-nine native species could—and could not—be found. More than two thousand amateur lepidopterists participated, and in 1984, the results were collated into a hundred-and-fifty-eight-page atlas. Every species got its own map with different colored dots showing the number of times it had been sighted in any given ten square kilometers. In the map for Polygonia c-album , the Comma’s range was shown to extend from the south coast of England northward to Liverpool in the west and Norfolk in the east. Almost immediately, this map became out of date; in the years that followed, hobbyists kept finding the Comma in new areas. By the late 1990s, the butterfly was frequently being sighted in the north of England, near Durham. By now it is well established in southern Scotland, and has been sighted as far north as the Scottish Highlands. The rate of the Comma’s expansion—some fifty miles per decade—was described by the authors of the most recent butterfly atlas as “remarkable.”
    Chris Thomas is a biologist at the University of York who studies lepidoptera. He is tall and rangy, with an Ethan Hawke-style goatee and an amiably harried manner. The day I met him, he had just returned from looking for butterflies in Wales, and the first thing he said to me when I got into his car was please not to mind the smell of wet socks. A few years ago, Thomas, together with his wife, their two sets of twins, an Irish wolfhound, a pony, some rabbits, a cat, and several chickens moved into an old farmhouse in the town of Wistow, in the vale of York. The University of York has an array of thermostatic chambers where Commas are raised under temperature-controlled conditions, fed carefully monitored diets, and measured on a near-constant basis, but in the spirit of British amateurism, Thomas decided to turn his own backyard into a field lab. He scattered wildflower seeds he had collected from nearby meadows and ditches, planted nearly seven hundred trees, and waited for the butterflies to show up. When I visited the place in mid-summer, the wildflowers were in bloom and the grass was so high that many of the tiny trees looked lost, like kids in search of their parents. The vale of York is almost completely flat—during the last ice age, it formed the bottom of a giant lake—and from the yard Thomas pointed out the spires of Selby Abbey, built nearly a thousand years ago, and also the cooling towers of the Drax power plant, Britain’s largest, some fifteen miles away. It was cloudy, and since butterflies don’t fly when it’s gray, we went inside.
    Butterflies, Thomas explained after putting the kettle on for tea, can be divided into two groups. First, there are the “specialists,” who require specific—winsome cases, unique—conditions. These include the Chalkhill Blue ( Polyommatus coridon ), a large, turquoise butterfly that feeds exclusively on horseshoe vetch, and the Purple Emperor ( Apatura iris ), which flies in the treetops of well-wooded areas in southern England. Then there are the “generalists,” who are less picky. Among Britain’s generalists, there are, in addition to the Comma, ten species that are widespread in the southern part of the country and reach the edge of their range somewhere in the nation’s midsection. “Every single one has moved northward since 1982,” Thomas told me. A few years ago, together with lepidopterists from, among other places, the United States, Sweden, France, and Estonia, Thomas conducted a survey of all the studies that had been done on generalists that reach the upper limits of their ranges in Europe. The survey looked at thirty-five species in all. Of these, the scientists found, twenty-two