RARE BUTTERFLIES IN OUR ISLANDS

 

In 1998, the ISLAND MARBLE (Euchloe ausonides insulanus), thought to be extinct since 1908, was discovered during a prairie butterfly survey at American Camp on San Juan Island. The only known specimens had previously been found on Vancouver Island and Gabriola Island in British Columbia. Scientists now believe American Camp, along with scattered locations on San Juan and Lopez islands, to be the only viable population in the world. This finding is based on multiple studies and monitoring since 2008. 

Scientists believe there are only about 200 of these butterflies left in the wild.

The Island Marble  does not migrate and is only known to now be found only in our San Juan Islands. It lives its entire life cycle in upland prairie-like habitat, but prairies, like the butterfly itself are becoming rarer and rarer. It is also found in sand dunes or coastal lagoon habitat.

The Island Marble’s wings have a fascinating color scheme of marbled green and white. It feeds on the flowers of  wild mustard. It has a wingspan of between 1.5 and 2 inches, and the caterpillar is about 3/4 of an inch long. It is green or blue-gray and dotted in black with white with yellow stripes down its back and sides. The marble butterfly can be confused it with the more common Cabbage White, which is mostly white with a yellow underside and feeds on the same plants.

After their long overwinter, the butterflies emerge from their chrysalis but only fly for 6-9 days, which means, the butterflies spend their time feeding, finding their mates to fertilize eggs, and then laying the eggs of the next generation.

 It will lay its eggs on two non-native mustards, field mustard (Brassica rapa) and tumble mustard (Sisymbrium altissimum). Virginia pepperweed (Lepidium virignicum) is the only native plant they will successfully lay eggs on.

The park has established a captive breeding program at American Camp where butterflies are reared and then reintroduced into the prairies. It is approximated that only 5% of eggs laid each year will survive to become adult butterflies. And yet the discovery of this lovely butterfly is a symbol of hope in a world where so many species are disappearing.

 Another butterfly found in our islands, which is not as rare as the Island Marble, but is considered  regionally rare, is the imperiled PROPERTIUS DUSKYWING (Erynnis propertius), a chocolate-brown skipper found only on the Pacific Coast of North America. Most of the Duskywings in Washington state are found in San Juan County, principally on San Juan Island. It is classified as a state Species of Greatest Conservation Concern.

The Duskywing is the only animal species that cannot survive without Garry Oak trees. Adult butterflies, which emerge in May, mate around oak trees and lay their eggs on the leaves. The caterpillars then roll themselves up in leaves to pupate. The leaves fall to the ground in the autumn with the pupae, still rolled up inside, stay dry and safe through winter, awaiting spring.

Duskywings are threatened by climate change and the loss of Garry Oaks, which is expected to shrink even more over the next century. Unlike the Island Marble, the Duskywing does not limit its food supply and feeds on many varieties of flowers.

 Several dozen old oaks remain at Mount Young (elevation of 650'), where they support most of the island’s Duskywing population. A few Duskywings have been seen on the south of Turtleback Mt. on Orcas Island. While the major part of the San Juan Island Duskywing population is still likely to be in the National Park, small numbers of these butterflies may establish in Garry Oaks elsewhere on the island, and care should be taken not to disturb fallen oak leaves until June.  Burning, and bagging leaves are to be avoided, as well as any spraying near the oaks.