The Island Marble

Butterfly back from the brink

After the miraculous rediscovery of a species once thought to be extinct, the rush to conserve the new population has begun.

In 1998, it was discovered that the once thought to be extinct Island Marble Butterfly was back within the San Juan Islands. The Island Marble (Euchloe ausonides insulanus) was only widespread throughout Vancouver Island and British Columbia but due to loss of habitat, predation, and anthropogenic impacts, the species was believed to be extinct in 1908. 100 years later, several sightings were reported on San Juan and Lopez islands. The San Juan Islands were not traditionally considered part of the Island Marble’s geographic range but this resurgence suggests that there could be a viable population protected among the islands. According to extensive surveys within six counties and sixteen islands done between 2005-2010, researchers located twenty-six areas where the butterflies were found. Among these, five were singled out as core populations. The more recent data of 2017 found that there are fewer than 200 adult individuals within these regions. Despite the population going from previously extant to having 200 individuals, the Island Marble is nowhere out of the woods yet.

The Island Marble is a member of the “white” family of butterflies and has a marbled white, yellow, green pattern on its wings. Island marble butterflies only live for about a year and spend most of that year within a chrysalis, a cocoon made by the island marble caterpillar where the stages of development take place for the butterfly to emerge in the spring. The butterfly only flies, mates, and lays eggs in the spring so those looking to research or spot the species must look then. The island marble will live its entire lifecycle in just one area of habitat. This ranges from prairie-like habitat, sand dunes, or coastal lagoon. Among these different habitat areas, the butterfly relies on plants within the mustard family for supplying a place to lay eggs and provide larval food. The island marble used to depend on native mustard species but now has shifted towards non-native mustards such as Brassica and Sisymbrium as the native plants have dwindled. The competition the non-natives bring make it difficult for the native plants to survive but the island marble’s ability to use either will be extremely beneficial to its recovery.

The island marble’s recovery plan recently took a turn for the best as the species was listed as an endangered species under the Endangered Species Act (ESA) on May 5, 2020. This protection means that there will be the development of a conservation plan and hopefully an eventual recovery of the species throughout the San Juan Islands.