Keith Van Cleve

The Island Marble began reappeared at American Camp in 1998 after more than 100 years.

The reappearance of the rare Island Marble butterfly on San Juan Island after more than 100 years continues to intrigue researchers and enthusiasts throughout the country.

In 1998, the Island Marble (Euchloe ausonides insulanus), thought to be extinct since 1908, was discovered during a prairie butterfly survey at American Camp. The only known specimens had previously been found on Vancouver Island in British Columbia.

Scientists believe American Camp, along with scattered locations on San Juan and Lopez islands, to be the only viable population in the world. At this point, the Island Marble is not listed as an endangered species, but efforts are ongoing to protect it.

“The presence of the butterfly is of great importance,” said Chris Davis, resource manager at San Juan Island National Historical Park. “Its survival here hangs in the balance.”

A study underway at American Camp and Friday Harbor may provide new insights into the natural history of the butterfly, including how far it flies, how long it lives and whether gender ratios vary in different areas.

This summer Dr. Merrill Peterson, a biology professor and entomologist at Western Washington University, will capture, mark, release and later recapture butterflies at three sites: two at American Camp and another in Friday Harbor. The U.S. Fish and Wildlife Service is sponsoring the survey in partnership with San Juan Island National Historical Park.

Within the park, Dr. Peterson has established rectangular units of measurement called “transects” in the dunes east of Pickett’s Lane and near Eagle Cove at American Camp, in addition to the abandoned gravel pit near Pear Point.

NPS Photo

A study underway at American Camp may provide new insights into the natural history of the Island Marble butterfly.

“We already have some idea about what the Island Marbles eat, where they lay their eggs and how long it takes for eggs to become caterpillars,”Davis said. “Hopefully we’ll be able to reach some conclusions about how to estimate populations through the catching and marking study.”

Davis said the next step will be to determine if it can adapt to feeding and laying eggs on native rather than the nonnative mustards it is currently utilizing at American Camp. The answers to these questions will be critical in determining whether or not the park incorporates native mustard plants into its ongoing prairie restoration plan.

“The goal of restoration is to control nonnative plant species, and at the same time, safeguard the Island Marble butterfy,” said Davis.

The Island Marble is white and pale green, with a mottled pattern of greenish- yellow under its hind wings. Look in the grassy prairie near wild mustard plants. Don’t confuse it with the more common Cabbage White, which is mostly white with a yellow underside and feeds on the same plants.