At Risk: Great Basin Silverspot
Female Silverspot Butterfly (Robb Hannawacker)
The Great Basin silverspot butterfly (Speyeria nokomis nokomis) has a fairly restricted distribution in eastern Utah, western Colorado, northern New Mexico, and northeastern Arizona.
Essential habitat components include wetlands associated with flowing water (i.e., springs, seeps, wet meadows), an abundance of their larval foodplant (e.g., bog violet [Viola nephrophylla]), and the availability of adult nectar sources (mostly composites) during the adult flight.
In the arid Southwest, these habitat conditions are widely separated and isolated; therefore, butterfly colonies are small and isolated. Great Basin silverspot butterflies do not migrate, but they are strong fliers and able to move among colonies within a continuous riparian corridor.
Nokomis fritillary males spend most of the day searching for females in the meadows or seeps that support their colonies.
Larvae of members of the genus Speyeria are generally thought to be nocturnal, feeding at night and resting during the day in a hidden location that is usually away from the host plant. They only consume bog violet plants. The tiny, unfed larvae must survive the harsh conditions of winter and then locate freshly emerging violet leaves before exhausting their limited reserves.
The Nokomis fritillary is associated with the Upper Sonoran (pinyon-juniper, various shrubs) and Canadian (fir-spruce-tamarack, some pine, aspen-maple-birch-alder-hemlock) habitats.
Great Basin silverspot butterflies utilize a variety of plant species as nectar sources, but thistles are strongly favored.
Bog violet
Why is it at Risk?
Modifications to hydrology (e.g., water diversion projects, capping springs, and draining wetlands), housing developments, and mineral extraction (e.g., gravel mining) have all contributed to further habitat loss and fragmentation.
Excessive livestock grazing is a threat to Great Basin silverspot butterflies by degrading their habitat and eliminating nectar sources, but light to moderate grazing may actually benefit the butterflies by giving a competitive advantage to their larval foodplants.
The Navajo Nation has given the Great Basin silverspot butterfly a Group 3 designation (i.e., prospects of survival or recruitment are likely in jeopardy in the foreseeable future), which gives it legal protection as an endangered species.
What you can do
Ranchers use prescribed fire to improve grazing by opening up the herbaceous understory. It can also be a valuable tool for maintaining habitat used by Great Basin silverspot butterflies, enhancing their larval foodplant populations, and increasing the flowering of important nectar sources. Negative effects of fire can include direct mortality of larvae in the litter layer during dormant season burns.
Light to moderate grazing has been shown to benefit Great Basin silverspot butterflies by giving a competitive advantage to their larval food plants, but sustained and intense grazing can degrade habitat and eliminate nectar sources during the adult flight.
