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 A Compton tortoiseshell butterfly suns itself in the Bonanza Creek Experimental Forest near Fairbanks. Photo by Ken Philip.
A Compton tortoiseshell butterfly suns itself in the Bonanza Creek Experimental Forest near Fairbanks. Photo by Ken Philip.

The Compton Tortoiseshell Flutters Northward

During the past 20 years, Ken Philip has driven 240,000 miles in his 1984 GMC pickup in search of the northern butterfly. From Hyder to Inuvik, he has chased down most of the 85 species that live up here, but the Compton tortoiseshell came to him.

The Compton tortoiseshell is a palm-sized butterfly that people had long reported seeing in Haines and southcentral Alaska but never north of the Alaska Range. In July 2002, Fairbanks entomologist Jim Kruse saw and collected a Compton tortoiseshell at the Bonanza Creek Experimental Forest southwest of Fairbanks. Intrigued, Philip “hotfooted down there” and captured a few with his wooden-handled net. He returned to Bonanza Creek again in 2003 and saw dozens of Compton tortoiseshells.

“They were all over the place,” he said. “It’s a very strange feeling to see a large butterfly we’ve never seen before, and for it to be so common.”

Philip is an independent researcher who retired from a career in radio astronomy in the 1970s to pursue northern butterflies. In the decades since, he has become Alaska’s butterfly expert, building a collection of more than 100,000 butterflies and moths. At age 71, he is still piling up mileage on northern highways in pursuit of one of the north’s most delicate creatures.

The appearance of the Compton tortoiseshell in Interior Alaska could be due to a few reasons, Philip said. One is that he may have missed the butterflies in past years as they sunned themselves on the packed dirt roads of Bonanza Creek Experimental Forest, and those elusive butterflies have since undergone a population explosion. Another possibility is that the butterflies migrated northward from elsewhere in Alaska, fluttering en masse through passes in the Alaska Range. The butterflies may have survived a series of mild winters to make a go of it farther north, like a tree seed that rides wind currents poleward and colonizes the soil exposed by a retreating glacier.

By mid-November 2003, Compton tortoiseshells and other Interior Alaska butterflies were hiding from the sting of 30-below zero air, waiting for the warm days of spring to emerge from their winter hiding spots. Hibernating adults often wedge themselves into tiny cracks in tree bark or other snow-covered crevices for protection. The butterflies can survive air temperatures as cold as minus 40 F, but they need snow to insulate them from colder air.

The butterfly is one of the most ephemeral of all creatures that make a living in the north. Some butterflies live for only 12 months, and they spend seven of those months locked in hibernation. Some butterflies that live north of the Brooks Range have actually extended their hibernation for an extra year to avoid rainy and cool summers. Regardless of how long they hibernate, a few weeks after they emerge from the long sleep to stretch their wings and lay eggs, they are dead.

Are the Compton tortoiseshells that showed up at Bonanza Creek another indicator that the north is getting warmer, or just a curious blip on the evolutionary radar? Philip isn't sure, but he knows that in 38 years of chasing northern butterflies in his truck, bush planes, helicopters, and boats, the Compton tortoiseshell is the first butterfly that made his trek shorter by traveling north.