Federal wildlife officials want to protect a rare white and green butterfly found only on Washington's San Juan Island.

The U.S. Fish and Wildlife Service says the island marble butterfly has been declining since it was rediscovered on the island in 1998. The agency is proposing to list the butterfly as endangered and to designate about 813 acres of mostly public land on San Juan Island as critical habitat for them.

The agency says the last remaining known population of island marble butterflies is on American Camp, part of San Juan Island Historical Park.

Surveys in 2017 found fewer than 200 adults.

The butterflies were once found on or near Vancouver Island in the 19th century, but weren't spotted for 90 years. A state zoologist rediscovered the butterfly on San Juan Island in 1998.

Other white butterfly species in the San Juans include the Cabbage White (Pieris rapae), Sara Orangetip (Anthocharis sara), and the Pine White (Neophasia menapia).