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.  

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.

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

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.

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.