Kevin Burls, Xerces Society for Invertebrate Conservation, (775)-273-8604, [email protected]
Matthew Forister, University of Nevada, Reno, (775) 784-6770, [email protected]
PORTLAND, Ore.; October 3, 2023—The Xerces Society for Invertebrate Conservation has submitted a petition for the U.S. Fish & Wildlife Service to protect several subspecies of the large marble butterfly, Euchloe ausonides, under the Endangered Species Act.
The large marble butterfly is found in 16 states ranging from Alaska to New Mexico and as far east as Michigan. Despite its widespread distribution, studies have ranked the large marble as one of the western butterfly species most at risk of extinction in the next 50 years. Large marble populations are threatened by widespread habitat degradation, introduced predators, pesticide exposure, climate change, and inadequate regulation across the states in which it is found.
“Large marble butterflies are important parts of ecological communities across the West, feeding on plants as caterpillars, pollinating flowers they visit as adults, and serving as food for everything from other insects to reptiles, birds, and mammals,” said Kevin Burls, an endangered species biologist with the Xerces Society. “Their disappearance on the landscape would be deeply felt.”
California’s large marble butterfly is the most imperiled
One large marble subspecies, Euchloe ausonides ausonides, is of particular concern, in danger of extinction in almost the entirety of its present range. The petition requests this subspecies be listed as Endangered.
Once present throughout each county in the Sacramento Valley and San Francisco Bay regions, most remaining populations are relegated to beachfront areas along the San Francisco Bay and in the foothills of Coast Range and Sierra Nevada mountains. Multiple long-term butterfly population monitoring sites have documented the disappearance of this butterfly subspecies, while new appearances in museum and photographic records in multiple regions have plummeted by over 80%.
If listed, this would be the second subspecies of this butterfly to be protected as Endangered under the ESA. The island marble, Euchoe ausonides insulanus, was petitioned in 2002 and again in 2012, and received protection and critical habitat designation in 2020.
Large marble butterflies throughout the West are under threat
The Xerces Society’s petition also requests that five additional subspecies (E. a. coloradensis, E. a. mayi, E. a. ogilvia, E. a. palaeoreios, and E. a. transmontana) are listed as Threatened. All of the populations have been declining.
“The decline of the large marble butterfly is part of a disturbing trend across the butterflies of the western United States. Species that were once common and widespread even a couple of decades ago are disappearing in many areas and being reduced to very low numbers in others,” said Matt Forister, a professor of biology at the University of Nevada, Reno, who has researched western butterfly population trends. “The large marble joins the monarch, the west coast lady, and other western butterflies that face an uncertain future and are deserving of conservation attention.”
As a widespread and historically common species, the large marble butterfly is an important part of western landscapes. Large marble caterpillars feed on various plants in the mustard family, and adults are medium-sized butterflies known for the complex of green swirls with white spots (“marbling”) across the entire hindwing on the undersides.
“ESA listing for the large marble butterfly, especially in California, is needed to protect this butterfly from becoming a permanent victim of the dangers butterflies face across western landscapes, including temperature increases and drought,” said Burls.
Individuals who want to contribute to the recovery of large marble butterflies, including farmers, ranchers and private landowners, can learn more from the Xerces Society or visit the U.S. Fish and Wildlife Service website for more information on the petition process.