Now that Canada Day has passed, a dedicated band of volunteers are heading for field and fen to begin the enumeration of those Canadians who are members of the order Lepidoptera: The great butterfly census of July has begun.
In Prince Edward County, an island on the northeastern shore of Lake Ontario, someone will be sucking in his breath at a giant swallowtail, a bruiser with a 15-centimetre wingspan. They are the largest butterflies in Canada and the United States - ravishing black-and-yellow animals that graze among the goldenrod and milkweed. Until a few years ago, their Canadian range was a pocket of exotic forest in the extreme south of Ontario, but for a variety of possible reasons - warming climate; the spread of their larval food plants, the prickly ash and the hop tree - their range has drifted east and north. The census-takers will find out if they are ranging farther.
Some of those who study butterflies see a darkening future for the insects and, by extension, for all life. In Britain, where butterflies and moths have been studied more intensively than anywhere, an accelerating decline in abundance from habitat loss has led experts to extrapolate a dreadful cull of species generally.
"If insects elsewhere in the world are similarly sensitive," nine scientists wrote in the journal Science, "the known global extinction rates of vertebrate and plant species have an unrecorded parallel among the invertebrates, strengthening the hypothesis that the natural world is experiencing the sixth major extinction event in its history."
The British study found that over 20 years, 71 per cent of all butterfly species had declined. Birds and plants declined as well, but butterflies fared worst of all. In a trope coined by Sandy Knapp, a scholar at London's Natural History Museum, Britain is the canary in the coal mine for the rest of the world, with effects detected in that country likely to turn up elsewhere. The best way to watch for this is to go out and count.
Known as the Canada Day count, the tallies actually take place on, before or after July 1. They provide a snapshot of numbers of species and butterfly abundance across a span of time when the insects are likely to be flourishing.
Each census covers the area of a 24-kilometre-wide circle. The Toronto West count, set for next Saturday, includes urban streets, the peninsula of the Leslie Street Spit, High Park and the scruffy, butterfly-rich strips of unused railway lines. Among newcomers from the south are the little yellow and the fiery skipper. The silvery blue, now an established colonist, arrived from the other direction. "They pushed down from the north," says John Carley, the leader of the Toronto West count, "following the spread of their food supply, crown vetch."
At the other end of town, the Toronto East count, led by Tom Mason, plunged into the Rouge River Valley and assorted creeks on July 1 and came up with 43 species, including 36 tiger swallowtails, 176 little wood satyrs and a painted lady. There were no silvery checkerspots, but none was expected: They vanished from Taylor Creek eight years ago. Nor was there a meadow fritillary, which Mr. Mason used to find in the Rouge.
Peter Hall, a research associate at the Canadian National Collection of Insects and one of the authors of Butterflies of Canada, leads a count west of Ottawa and has found 70 species over the years. These days, the haul could include a Delaware skipper, not seen in Eastern Ontario until 1998, when Mr. Hall found the first.
"I could take you out right now," he says, "and find it at 15 locations."
The census area also contains an unusual, limestone habitat called an alvar that attracts the mottled duskywing, a kind of butterfly known as a skipper for its rapid, darting flight. The mottled duskywing has a striking purplish gloss and light yellow-brown highlights on the wings. It is rare in Canada and may soon be listed as endangered.
