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Only a single population remains.


Expert Contact:

Scott Black, Executive Director, Xerces Society for Invertebrate Conservation
(503) 449-3792  |  [email protected]

PORTLAND, Ore.; May 5, 2020---In response to a petition filed by the Xerces Society in 2012, today the U.S. Fish and Wildlife Service (USFWS) finalized listing the island marble butterfly (Euchloe ausonides insulanus) as an endangered species under the Endangered Species Act (ESA) and designated critical habitat.

The Xerces Society and other conservation groups first petitioned the USFWS to protect the island marble butterfly as an endangered species in 2002. In 2006, the USFWS denied protection to the butterfly citing voluntary conservation efforts. When monitoring by the Washington Department of Fish and Wildlife and others indicated that the butterfly’s populations were continuing to decline, the Xerces Society again petitioned the USFWS in 2012.

“We are so glad to see the island marble butterfly finally protected,” said Scott Black, Executive Director of the Xerces Society. “But we are highly disappointed that it took 18 years to get the protection it deserves.”

When the Xerces Society first petitioned for this butterfly’s protection, it was found at multiple sites, including populations on both Lopez and San Juan islands. Unfortunately, the island marble now only occurs in one population within American Camp National Park on San Juan Island, which makes recovery much more difficult.

The island marble faces many threats, including:

  • Habitat loss and degradation from plant succession and invasion by plants that displace larval host plants; browsing by black-tailed deer, European rabbits, and brown garden snails; and storm surges;
  • Road maintenance, mowing, removal of the host plants it’s caterpillars need, and restoration activities that are improperly timed;
  • Predation by native spiders and nonnative wasps, and incidental predation by black-tailed deer; and
  • Vulnerabilities associated with small population size and environmental and demographic stochasticity, and other chance events that increase mortality or reduce reproductive success.

In 2019, the USFWS approved a Programmatic Candidate Conservation Agreement with Assurances (CCAA) for the island marble butterfly in San Juan County, Washington. The CCAA is a voluntary agreement with landowners to promote conservation that reduces threats and provides for voluntary action to help recovery. Many landowners have signed up for the CCAA, which could give this butterfly a chance at survival.

“We hope that now the island marble is listed funding can be made available to help the butterfly recover,” said Scott Black. “If we can act quickly, our grandchildren might still be able to experience this wonderful animal.”




To read the 2012 ESA petition submitted to the USFWS,

For photographs from the USFWS Pacific Region,



The Xerces Society is a nonprofit organization that protects the natural world by conserving invertebrates and their habitat. Established in 1971, the Society is a trusted source for science-based information and advice and plays a leading role in promoting the conservation of pollinators and many other invertebrates. We collaborate with people and institutions at all levels and our work to protect bees, butterflies and other pollinators encompasses all landscapes. Our team draws together experts from the fields of habitat restoration, entomology, plant ecology, education, farming and conservation biology with a single passion: Protecting the life that sustains us.

To learn more about our work, please visit or follow us @xercessociety on Twitter, Facebook or Instagram.