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On Oblivion's Edge

Unseen for 90 years, a unique butterfly emerges and causes a stir

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COURTESY OF KEITH VAN CLEVE The Island Marble butterfly has re-emerged on San Juan Island, prompting the National Park Service to rethink its restoration plan for the prairie lands where it was discovered.

The Island Marble butterfly stirred plenty of emotion when it was rediscovered on San Juan Island in 1998.

Excitement, because the Island Marble, which hadn't been seen since 1908, was believed to be extinct. Trepidation, that news of the Island Marble's discovery would invite interest that could jeopardize its survival. Awe, because a subsequent survey in San Juan County — the first ever — identified 44 species of butterflies on the islands, more than most other areas of similar size in the Northwest. Frustration, because the National Park Service is restoring a coastal prairie where the Island Marble was discovered, and now must accommodate the non-native butterfly and its non-native host plants at the same time it is eradicating other non-native animals and plants.

The challenge is not lost on Peter Dederich, superintendent of San Juan Island National Historical Park. Dederich is overseeing the prairie restoration at the park's American Camp, one of two sites used by American and British troops during the joint military occupation of the island from 1859 to 1872 while ownership of the island was in dispute. To restore the prairie, Dederich must get rid of European rabbits, descendants of those imported to the island for food in the 1880s. The rabbits have stripped the prairie of native grasses, and their burrows have disturbed sand dunes and culturally sensitive sites.

Dederich estimates that it will take 50 years to restore the prairie. The National Park Service has begun by eradicating non-native plants through controlled burns. It is also planting native grasses. Island Marbles depend on rape and tumble mustard, both of which were introduced to the island for grazing; Dederich hopes to reintroduce indigenous beach mustards on which the Island Marble can feed and lay its larvae.

"It's a tough situation," Dederich says. "We don't know what the native prairies looked like. But it's clear (the Island Marble) survived before non-native mustards. The Island Marble was common in Prospect Park in Victoria in the 1800s. And they weren't living on non-native mustard there."

The Island Marble was historically found in British Columbia — on Gabriola Island and on Vancouver Island from Nanaimo to Beacon Hill Park in Victoria, according to a petition to put it on the U.S. endangered species list. It was last recorded on Gabriola and Vancouver in 1908, and just 13 specimens remained to tell of it. Experts think most likely it disappeared after grazing cattle eliminated its larval food sources.

Then in spring of 1998, the Island Marble was rediscovered. Zoologist John Fleckenstein was looking for butterflies at American Camp when he saw an unfamiliar, white and greenish butterfly drinking nectar. "I didn't realize I found something important," Fleckenstein recalls.

Fortunately, the Northern Lapidopterist Society was meeting in Eugene, Ore. Fleckenstein dispatched an assistant to the meeting with a specimen.

Fleckenstein's discovery rocked the meeting. Today, the Island Marble is included on the petition, filed by a coalition of environmental and scientific organizations, asking the U.S. Fish and Wildlife Service to put the butterfly and 11 other insect and animal species on the federal endangered species list. Should the Island Marble be declared an endangered species, the National Park Service would "have to give the butterfly some consideration" in its habitat and vegetation management at American Camp, Fleckenstein says. But even without the listing, Dederich is working to accommodate this unique butterfly.

For now, plants that the Island Marble uses are being given a wide berth. Dederich and state biologist Ann Potter have asked park neighbors to watch for the butterfly and to let mustards grow on their land. "We're going to work to enhance the butterfly population regardless if it is declared an endangered species," Dederich says.

While doing a survey in 2003, zoologist Robert Pyle found an Island Marble nectaring on an indigenous beach mustard. Pyle believes the butterfly could have been a beachcomber drawn inland by the smaller mustards introduced for grazing. "And if the beach population represents the aboriginal condition on San Juan Island, the upland and headland population of today might have been founded by wanderers having discovered and colonized introduced mustards," Pyle theorized in a report to the National Park Service.

In any case, seven years after its discovery, the Island Marble is expanding its habitat. San Juan Island was believed to be the butterfly's only home until this year. In a recent survey of 120 sites in North Puget Sound, Island Marbles were observed at two places on neighboring Lopez Island. Fleckenstein says the Island Marble's population could be as high as 1,000, but it still leads a precarious existence. The larvae are hosts for parasitic wasps; the adults are prey for birds, robber flies, dragonflies and spiders. A county road crew unwittingly mowed mustards on a Lopez Island roadside where Island Marbles had been observed nectaring.

"Even in healthy populations, it can fluctuate from year to year depending on weather conditions," Dederich says.

So why does this matter? Aside from being food for other creatures, Island Marbles help with pollination, Fleckenstein says, adding that they may also act as controls on some weeds. And, they likely serve functions we don't yet understand, he says. But for him personally, "their greatest value is aesthetic. To know they are there carries a lot of weight for me."

Molly and Richard Walker are freelance writers living near Island Marble habitat on San Juan Island.