FWS Focus

Overview

Characteristics
Overview

Once thought to be extinct, the island marble butterfly was rediscovered by biologists during a survey on San Juan Island, Washington in 1998. The island marble is a member of Pieridae, known as the white family of butterflies, and primarily consisting of white and yellow butterflies. It is recognized as a subspecies of the large marble (Euchloe ausonides) based on physical and behavioral differences. Because there are so few of these butterflies left, possibly as low as 300 individuals, the population is particularly vulnerable to anything that causes butterfly death or reduces their ability to reproduce. Habitat for the island marble is degraded by natural succession from prairie-like habitat to woody plants and trees, as well as invasive plants. 

Scientific Name

Euchloe ausonides insulanus
Common Name
Island marble Butterfly
FWS Category
Insects
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Habitat

Characteristics
Habitat

The island marble butterfly does not migrate and is only known from the San Juan Islands in Washington State. It lives its entire lifecycle in upland prairie-like habitat, sand dunes or coastal lagoon habitat. The butterfly primarily uses two non-native plants and one native plant of the mustard family as their larval host plants. The species appears to have developed the capacity to use non-native mustard plants that readily colonize the open prairie-like habitat and sand dunes in addition to the native mustard plant. Regardless of how this development may have occurred, the use of non-native plants like field mustard and tumble mustard has contributed to the survival of the island marble in upland habitat and is expected to continue to play a significant role in the species continued existence.  

Grassland

Ecosystem with large, flat areas of grasses.

Characteristic category

Physical Characteristics

Characteristics
Color & Pattern

The upper, or dorsal, side of the island marble butterfly’s wings are creamy white with black markings, while the yellow-green marbled pattern on the lower, or ventral, side of their wings are what give the subspecies its name.

Size & Shape

The island marble is 1.75 inches long, which is slightly larger than other subspecies of marble butterflies.

Characteristic category

Lifecycle

Characteristics
Lifecycle

Island marble butterflies are most visible in the spring when they are winged adults, but for the rest of the year they are present as either eggs, larvae or chrysalises, the butterfly version of a cocoon. Island marble butterflies spend most of their year-long life as a chrysalis waiting for the right environmental cues to undergo metamorphosis and emerge as a winged adult. One island marble butterfly was documented as being a chrysalis for 334 days!

After an island marble butterfly emerges from its chrysalis, it immediately mates and lays eggs, living less than a week before dying. The eggs of the island marble are barely a millimeter tall and are initially a faint bluish-green to cream-colored, changing to reddish-orange just prior to hatching. Upon hatching, island marble butterfly caterpillars rapidly progress through five distinct developmental larval stages, known as instars, and each instar is characterized by specific color patterns. Immediately prior to developing into a chrysalis, island marble butterfly caterpillars wander around searching for a safe location to over-winter in chrysalis form. As a chrysalis the island marble resembles a small dried up seed pod making them nearly impossible to see when over-wintering, hidden until emerging as adults the following spring. The island marble butterfly only flies and lays eggs in the spring of the year.

Characteristic category

Food

Characteristics
Food

Island marble butterfly larvae feed on their three known larval host plants. While adult island marble primarily feed on those plants, they also forage on a variety of nectar plants such as yarrow, small-flowered fiddleneck, field chickweed, common lomatium, california buttercup and native prairie plants.

Geography

Characteristics
Range

Until 1998, the island marble butterfly was only known from historical collections made on Vancouver Island and the Canadian Gulf Islands in British Columbia, with 14 specimens collected from 1859 to 1908. These islands are part of the same geologic formation as the San Juan Archipelago, which is located immediately to the south of the Canadian Gulf Islands. The island marble butterfly had been last collected on Gabriola Island, Canada, in 1908 and was considered extirpated throughout its known range before it was rediscovered in 1998 in San Juan Island National Historical Park. Although the island marble was not previously documented on the San Juan Islands, it has likely been present in isolated locations in the islands throughout the last century. Extensive surveys were conducted from 2005 to 2010 that included six northern counties and 16 islands in Washington State. During this time period, 26 locations were determined to be occupied, representing five core populations, all on San Juan and Lopez Islands.

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