The region’s spate of long, hot days brought out the best of these beauties — Papilio troilus, the spicebush swallowtail like a shimmering tuxedo dancing down a wooded path, and the gaudily striped P. glaucus, the tiger swallowtail lured to the liqueur of garden Buddleia and roadside purple loosestrife blossoms.
But the specialty of the summer solstice and its lingering swelter was Papilio cresphontes, the tourist of the crowd, the giant swallowtail up from the Deep South, sampling these northern climes in a brief preview of climate change. In 2010 these extraordinary butterflies bought their season tickets for the third year in a row, and appear to have settled in for the duration. In the manner of monarchs, they have migrated north, laid eggs and produced a new generation.
My friend Steve Chorvas first told me about the giants in our midst late last year. He had seen them the year before here in Saugerties, north of the Village, up by the Great Vly and the limey clay flats where the caterpillar host plant of the giant thrives and grows. It’s the prickly ash (Zanthoxylum americanum), not really an ash, but a member of the citrus family, a relative of lemons and oranges. In the south the giant swallowtail can be a pest in orange groves, where its caterpillars — they look like bird droppings! — eat the leaves of orange trees. Down in Florida they call the caterpillars “orange dogs.”
Steve found orange dogs on roadside prickly ash shrubs last September. He raised them and they formed chrysalids, which survived the winter outside and emerged the next year in late spring. Past records of giant swallowtails breeding in New York appear to have been unsuccessful in establishing colonies lasting into the following year. But winters do seem to be getting milder, maybe mild enough to allow these southern visitors to become permanent residents.
Consider the giant swallowtail compared to butterflies commonly occurring in our area. The tiger and spicebush swallowtails are year-round residents here. Their caterpillars feed on common trees and shrubs in our region, and their chrysalids are well adapted to surviving our cold winters. The monarch is an oddball.
Though monarchs range as far north as Canada, they remain very successful migrants. Monarchs are strong fliers, with several summer generations pushing farther north over the season. The females lay eggs on milkweeds, which range well into Canada. Caterpillars grow fast on milkweed and form chrysalids from which adults emerge the fall and then head south to warmer climes, some individuals heading out as late as mid-October, off to Florida, the Gulf coast, to Mexico and those famous mountain forests where they hang from pine branches all winter, by the thousands, millions even. The monarch has its act together and it works.
The giant swallowtail is another story. It seems to be a species adapting to climate change, pushing at the edges of its limits of cold tolerance in a time of global or regional warming. Why do these magnificent insects wander northward year after year? Maybe the best answer is simply “because they can.”
Change keeps happening, and all too often these days, it’s not hopeful. But the prospect of a new member of our charismatic butterfly megafauna is spirit-lifting. ++