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Large Marble Butterfly ESA Petition FAQ

The large marble butterfly (Euchloe ausonides) was proposed for listing under the Endangered Species Act in 2023 through a petition submitted by the Xerces Society.

What is the large marble, and where is it found?

The large marble butterfly (Euchloe ausonides) is in the family of butterflies known as Pieridae. One of a few related “marble” species, it is named after the green patterning on the underside of the wings. The caterpillars feed on numerous plants in the mustard family, including some that are native to the United States and others that have been introduced. Caterpillars and adults are found in a variety of open habitats including grasslands, meadows, sagebrush steppe, montane slopes, and weedy flats. Some populations can be found in urban environments including parks or occasionally even weedy lots. The species’ range in the United States includes Alaska, California, Colorado, Idaho, Michigan, Minnesota, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming. The species does not occur in the rest of the United States.

Why does the large marble need Endangered Species Act (ESA) protection?

Populations of the large marble have declined since the 1980s in almost every place across its range where butterflies are monitored, including at sites in California, Oregon, Washington, Idaho, and Colorado. The most recent studies, which use data from long-term monitoring sites, suggest the large marble is one of the most imperiled species in the West, with possibly a 66% chance of extinction at these sites in the next 50 years. In addition, museum collections and photographic observations of butterflies from across the species’ range indicate the large marble is declining across 75% of its distribution, including in every state in which it is found.

Why are large marble populations threatened with extinction?

Populations of the large marble butterfly have declined drastically in so many places because they face multiple ongoing threats to caterpillars and adults, including habitat loss to agriculture and development, exposure to harmful pesticides, habitat degradation from multiple causes, introduced predators, and the effects of climate change. Human populations in many western states are expected to grow by 15% or more between 2020 and 2040, resulting in development that will continue to eliminate the open habitats preferred by the large marble butterfly. Large marble caterpillars feeding on mustards found along crop edges may be killed by herbicides, and the caterpillars and adults that use the plants are also vulnerable to insecticides meant for pests. Other populations occur on rangelands that may be degraded by overgrazing or other causes. These rangelands can be rich in non-native mustards but may be lacking other native caterpillar or adult food sources if proper rangeland management strategies aren’t being implemented.  Some rangelands are threatened by large-scale pesticide sprays to control particular pests. Finally, populations across western North America are threatened by the effects of climate change, including increased temperatures and decreased precipitation, which can stress all life stages of the butterfly and affect plant quality in natural landscapes. While it may be hard to pin the decline of the large marble on one particular threat across space and time, monitoring data has demonstrated that the large marble butterfly is one of the most threatened butterfly species in the West.

How will protecting the large marble as a Threatened Species under the Endangered Species Act help this butterfly?

Listing the large marble butterfly as Threatened under the Endangered Species Act will allow the U.S. Fish and Wildlife Service to create a recovery plan for the species and set guideposts for success. During the decision to list a species, the agency can also designate critical habitat to protect areas that are key to the large marble butterfly. In addition, Threatened species are eligible to have a 4(d) rule, which allows for more flexibility and may only include a set of restrictions on the activities and areas that are most critical to the declining species, as opposed to a prohibition on take across the butterfly’s entire range. Under Rule 4(d) of the Endangered Species Act, the U.S. Fish and Wildlife Service can also incentivize proactive conservation efforts by streamlining Endangered Species Act compliance for actions that have long-term benefits but might result in “take” in the short term. These 4(d) rules can help maintain and improve threatened species status to prevent further declines while simultaneously reducing undue regulatory burden.

Protection of the large marble subspecies Euchloe ausonides ausonides as Endangered, as requested in the petition, would include a variety of automatic prohibitions, including prohibitions on “take,” which means any attempt to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect" the species. These populations would not be eligible for an exemption under a 4(d) rule.

How would ESA protection for the large marble affect croplands?

Many of the large marble’s currently preferred habitats are not near croplands, and the butterfly does not occur in many areas dominated by row crops, including most of the Midwest. In places like central and eastern Washington, western Idaho, or central Montana where the butterfly is found on or near agricultural fields, listing the large marble as a Threatened species may mean that certain activities are exempted from the take prohibition through a 4(d) rule, which would be proposed by the U.S. Fish and Wildlife Service at the time of a proposed listing. In addition, the Endangered Species Act allows for voluntary agreements involving private or other non-Federal property owners whose actions contribute to the recovery of species listed as Threatened or Endangered. In exchange for actions that contribute to the recovery of listed species, participating property owners receive formal assurances, called a “safe harbor agreement,” that they will not be charged with violating any take prohibition that may be put in place. 

If the subspecies Euchloe ausonides ausonides is listed as Endangered, a take prohibition would exist. This would include populations in California’s Central Valley should the large marble be found there, although populations of this subspecies have not been seen in farming regions of the Sacramento Valley since the mid-2000s. In this case, voluntary agreements between landowners and the U.S. Fish and Wildlife Service could allow farmers in California to receive safe harbor agreements.

How might ranchers be affected if the large marble is protected through the ESA?

Many of the large marble butterfly’s caterpillar food plants are found on western grazing lands, including private property as well as property managed by the Bureau of Land Management (BLM) and U.S. Forest Service (USFS). If the large marble butterfly is protected as a Threatened species, certain ranching activities on public and private land may be exempted from prohibitions on accidental “take” under a 4(d) rule. In addition, the Endangered Species Act allows for voluntary agreements involving private or other non-federal property owners whose actions contribute to the recovery of species listed as Threatened or Endangered. Ranchers using conservation practices approved by the Natural Resources Conservation Service can also enter into a Working Lands for Wildlife conservation agreement to allow for incidental take of animals during the implementation of these practices.

If the subspecies Euchloe ausonides ausonides is protected as an Endangered species, a take prohibition would exist for these populations. The U.S. Fish and Wildlife Service would then consult with federal agencies (such as the BLM and USFS) when they take actions that may harm large marble butterflies or degrade their habitat. If a formal assessment determines that grazing is adversely affecting the large marble in these areas, voluntary agreements between private landowners or ranchers with public grazing leases and the U.S. Fish and Wildlife Service may allow ranchers in California to receive safe harbor agreements.

How might researchers and community scientists be affected by a listing of the large marble?

As mentioned above, listing the large marble as a threatened species allows for a 4(d) rule to be issued, which may exempt certain activities from the “take” prohibition if they are determined to not substantially threaten the species. For any research activities that will require a permit once this species is listed, the Xerces Society continues to recommend that the U.S. Fish and Wildlife Service streamline the permitting process in order to facilitate study by professional researchers, community scientists, and other amateur lepidopterists, recognizing the critically important role of these activities in species conservation. 

For the subspecies Euchloe ausonides ausonides in lowland California, projects on private lands involving federal permits or assistance will require review to ensure activities are not negatively impacting the species.

Why has the Xerces Society decided to petition one subspecies of large marble as Endangered and the rest as Threatened?

Populations of the subspecies Euchloe ausonides ausonides were historically found across low elevation areas central and northern California including all of the Sacramento River Valley and Delta regions, extending into the foothills of the Sierra Nevada mountain range. However, this butterfly has vanished from large sections of its range, including at many long-term butterfly monitoring sites in California’s Sacramento Valley. Extirpations of this subspecies have been documented at at least 4 monitoring sites in Sacramento, Solano, and Yolo Counties, and there are no observations in other Sacramento Valley counties for the last 15 years. Based on museum specimens and photos, the range of this butterfly has been reduced by over 30% and it is seen less frequently across the remainder of its range. Neonicotinoid pesticides used in agriculture have been associated with the loss of butterfly species at some of the long-term monitoring locations. 

Remaining populations of Euchloe ausonides ausonides are largely clustered around the San Francisco Bay region, with observations extending down the Monterey coast and the Sierra Nevada foothills. The majority of individuals in the San Francisco Bay are in or adjacent to highly urbanized environments including shoreline preserves, city parks, or foothills surrounding residential areas where its caterpillar and adult food plants can still be found. These populations are highly vulnerable to urban pesticide exposure and continuing loss of habitat from the destruction of its required caterpillar food sources. Without protecting the remaining populations of this subspecies from these threats, this butterfly could be gone from these landscapes in the near future. The first large marble subspecies to receive protection—the island marble, Euchoe ausonides insulanus—only remains at a couple of sites in the San Juan Islands in Washington and was petitioned in 2002 and again in 2012, and received protection and critical habitat designation in 2020. 

The remaining five subspecies of Euchloe ausonides would be listed as Threatened under the Xerces Society’s petition. These subspecies include the majority of large marble populations, which we know are declining in monitoring locations in the Pacific Northwest and the Rocky Mountains. Listing the large marble butterfly as Threatened will protect these populations from declining to the point where they begin to disappear across their entire range.

Map of Euchloe ausonides subspecies.


What is the process for this petition?

While some stages of the petition process occur more quickly than others, the entire process may often take years. 

  1. 90-day finding: From the date that a petition is filed, the U.S. Fish and Wildlife Service has 90 days, to the extent that it is possible, to make an initial finding on whether the petition has substantial information indicating that listing the large marble butterfly may be warranted. 
  2. 12-month review: If a positive 90-day finding is issued, Service biologists will conduct a 12-month, peer-reviewed status review of the species’ ecology, abundance, population trends, and threats to the species in order to evaluate the species’ current status and extinction risk. A review of conservation efforts is also completed. Following this, the Service will issue a final positive or negative finding on whether listing the large marble butterfly as Threatened is warranted. However, given the substantial workload of the U.S. Fish and Wildlife Service, 12-month findings can take longer than 12 months; the Service publishes a National Listing Workplan with a specific timeline of when 12-month findings will be completed for species that have been petitioned and have received positive 90-day findings. 
  3. Public comment period: If a 12-month finding determines that listing is warranted, the Service will solicit public comment and may hold public hearings. 
  4. Final ruling: Finally, after considering public input and any new additional information, the Service issues a final ruling, ideally within a year (but sometimes longer). Sometimes the species is listed immediately, but other times the species’ listing is precluded by higher priorities. In these cases, the species is listed as a Candidate for protection, as the monarch butterfly is currently.

What does the Xerces Society hope to accomplish by filing this petition for the large marble?

The Xerces Society is a science-based, nonprofit organization dedicated to the conservation of invertebrates and their habitats. We are named after the now-extinct Xerces blue butterfly. Recent studies have found that western butterfly communities are in a state of ongoing decline at a rate equivalent to losing 25% of the region’s butterflies every 30 years. While the monarch has received much-due attention for its decline, data from long-term butterfly monitoring programs have shown that many other butterflies are in a similar state of danger, including the large marble butterfly, which is one of the region’s top-five imperiled butterflies according to the most recent study. Our western butterfly initiative is dedicated to using the best available scientific evidence to protect and advocate for the West’s most imperiled butterfly species. 

Listing the large marble butterfly as a Threatened species is a critically important step to save the species from declining to the point of imminent extinction. Letting a once-common and widespread species like the large marble decline to the point of extinction would be yet another milestone in what is now recognized as an ongoing mass extinction event affecting all of life on earth. The Endangered Species Act is our nation’s most effective law for protecting animals and plants in danger of extinction, and it has prevented 99% of listed species from going extinct. Managing the habitat of existing populations and increasing the availability of additional high quality habitat will help reverse the ongoing declines this species is currently experiencing.

How can I help the large marble butterfly?

Large marble populations will benefit from actions that create and conserve high quality habitat across the butterfly’s range. Maintaining existing natural open areas including grasslands, meadows, and sagebrush, especially those with native host plants, is the easiest and most important step to conserve existing large marble populations. These habitats need host plants for caterpillars to eat, a safe space to pupate, and nectar flowers for adults, all free from pesticide residues. 

Note that the required host plants for large marble caterpillars are native plants in the mustard family. The mustard family is a large and diverse plant group that includes both native and non-native species. While some non-native mustards are considered weedy, several non-weedy mustard plants look similar to weedy ones, and as such are removed from the landscape. It is imperative that native mustard species be recognized, distinguished, and protected during land management and weed suppression activities. Vegetation management and weed suppression activities should always begin with precise plant identification. Finally, when carrying out restoration practices on landscapes invaded with native mustards, managing any landscape disturbances in sections, such as prescribed burns, will limit mortality of large marble caterpillars and adults feeding on non-native plants.

Additional native wildflowers provide important nectar resources for all butterflies. You can find native pollinator-friendly native plant lists for your area on the Xerces Society website, and there are additional resources available on creating habitat for butterflies.