A relatively large butterfly subspecies found only in western Colorado, northern New Mexico and far-eastern Utah would be listed for Endangered Species Act protection as a threatened species under a new U.S. Fish and Wildlife Service proposal.
The proposal for the silverspot butterfly follows completion of a peer-reviewed species status assessment prepared by the agency’s Western Colorado Field Office in Grand Junction.
“While the silverspot butterfly is not in immediate danger of extinction, the best available scientific information indicates that it is in danger of extinction in the foreseeable future,” the agency said in a news release.
The subspecies proposed for listing is one of five silverspot subspecies in the United States and Mexico. The three-state subspecies has been documented in 10 populations, including one in Mesa County and crossing into Grand County, Utah, made up of multiple colonies.
The subspecies has a wingspan up to 3 inches and is found at elevations between 5,200 to 8,300 feet, in moist, open meadows with vegetation for shelter. Its caterpillar feeds exclusively on bog violets found in such areas.
Primary threats facing the butterfly include habitat loss and fragmentation, climate change, incompatible livestock grazing, human alteration of natural hydrology that affects marshy areas, and genetic isolation between populations, the Fish and Wildlife Service says.
“With the butterfly being reliant on water to produce the bog violet and nectar sources, then a warming and drying climate is certainly of concern,” Terry Ireland, a biologist with the Western Colorado Field Office who is the Fish and Wildlife Service’s species lead for the butterfly at the office, said in an interview Tuesday.
One colony of the butterfly can be found in Unaweep Canyon, but a second colony in the canyon referred to as the Unaweep Seep colony appears to have disappeared.
“Unfortunately we have not seen any (silverspot) butterflies there the last five years,” Ireland said.
It’s also thought that the butterfly might have historically lived in the area of Rifle Gap Reservoir in Garfield County, where the reservoir and dam there may have degraded and fragmented its habitat. Construction of a golf course and homes in La Plata County caused the loss of two colonies there.
While the Fish and Wildlife Service sometimes designates critical habitat to protect imperiled species, it is choosing against doing so for the silverspot subspecies out of concern that it would only help alert butterfly collectors to where they could find the butterfly.
“There is a market for rare and kind of showy, colorful butterflies, which this silverspot species would fall into that category,” said Justin Shoemaker, a listing and classification biologist with the Fish and Wildlife Service’s Mountain-Prairie Region Office.
Ireland said a lot of collection occurred at the Unaweep Seep site and may have contributed to the butterfly’s decline there.
Collecting and selling the butterfly would be prohibited if it is listed as threatened, due to a prohibition against taking threatened and endangered species through means such as killing, harming and harassing them.
However, the Fish and Wildlife Service is proposing a rule allowing the incidental take of the butterfly in some cases, which it said in its release “would support tailored conservation of the species with balanced land management to allow continued acceptable land uses.” This would allow incidental take resulting in some cases from activities such as livestock grazing, haying or mowing, prescribed burning, and noxious weed control, as long as they occur in certain manners or times of year prescribed by the Fish and Wildlife Service. Ireland said grazing in certain conditions can be compatible with the butterfly’s needs, removing dead vegetation and helping the bog violet to prosper.
WildEarth Guardians had petitioned the agency in 2013 to list the species for protection under the Endangered Species Act.
“Listing offers silverspots a much-needed lifeline,” Joe Bushyhead, endangered species attorney with WildEarth Guardians, said in a news release Tuesday. “We’re hopeful the ESA can provide a path to both recover the butterfly and safeguard its vanishing habitat.”
The proposed listing and the accompanying rule pertaining to incidental take are open for a 60-day public comment period. More information may be found at https://www.federalregister.gov/public-inspection/2022-09446/endangered-and-threatened-species-status-for-the-silverspot-butterfly. The species status assessment for the butterfly may be found at https://www.fws.gov/sites/default/files/documents/20210211%20Final%20S.%20n.%20nokomis%20SSA%20Version%201_508.pdf.