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The Island Marble Butterfly: A Rare Little Beauty Fighting for Survival On San Juan Island

Scott McCarthy, U.S. Fish and Wildlife
Ecologist Ted Thomas says the Island Marble butterfly seeks nectar from its primary larval food plant, the nonnative field mustard.

An incredibly rare Northwest butterfly has been listed as a species that qualifies it for federal protection. It’s small, and at first glance, it's mostly white. It’s called the Island Marble butterfly. 

The only place it can be found in the world is American Camp, a national historic park on the southern end of San Juan Island. It derives its name from the iridescent design on the underside of its wings. It looks as though a marble dipped in shiny, lime green paint rolled on its surface.

Ted Thomas, an ecologist with U.S. Department of Fish and Wildlife says deer are the main threat to the species. They like to eat the same mustard plants the Island Marble lays its eggs on.

“So the deer, they’re focusing in on the same plant, sometimes the same bud that the island marbled butterfly just laid an egg on. And if they come along and chomp that same bud, it’s so long butterflies.”

As part of a legal settlement with the Xerces Society for Invertebrate Conservation, the Department Fish and Wildlife recently declared the Island Marble a candidate species.  

However, the federal agency says taking the next step to officially list the species as threatened or endangered is not possible right now. Thomas says resources are being spent on saving other plants, animals and insects that are in a similar situation as the Island Marble; but that have the additional threat of losing their habitat.

“Those are what we call high-priority listing actions. Because we may lose that habitat in one fell swoop. We could lose it in an afternoon’s activity if somebody is running a bulldozer,” said Thomas.

Thomas says a threatened or endangered listing for the Island Marble might be possible next year. For now, the agency is setting up eight-foot-tall fences around mustard plants to try and protect the Island Marble’s eggs from deer.

The Island Marble was thought to be extinct around the turn of the last century. Back then, small numbers of the butterfly were spotted on Vancouver Island. Then, it simply vanished. The next sighting of the species was in 1998 on San Juan Island. Ninety years had passed. Researchers are still trying to figure out the species’ reappearance.

Jennifer Wing is a Producer for our weekly show, Sound Effect.