Photo above: Female silverspot butterfly (Speyeria nokomis nokomis). Photo by Robb Hannawacker.
By Joe Szuzwalak
Earlier this week, the U.S. Fish and Wildlife Service proposed to list a subspecies of silverspot butterfly (Speyeria nokomis nokomis) as threatened under the Endangered Species Act (ESA). This proposal follows the completion of a peer-reviewed Species Status Assessment (SSA) that is also available today.
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.
While there are various ‘silverspot’ butterflies, this subspecies has been documented in ten populations across southwestern Colorado, eastern Utah, and northern New Mexico, ranging in elevation from 5,200 to 8,300 feet. A relatively large butterfly with up to a 3-inch wingspan, silverspot butterflies are known for distinctive silvery-white spots on the underside of their wings. On their upper side, females have a cream or light-yellow coloring with brown or black, and males have a bright orange upper side.
The silverspot requires moist, open meadows with vegetation for shelter. Herbaceous plants are also important for nectar sources, which provide energy to adults for mating and flying. This butterfly has an annual life cycle and lays eggs on, or immediately next to, the bog violet (Viola nephrophylla/V. sororia var. Affinis) that the larvae feed on exclusively. The eggs hatch approximately two weeks after being laid in September and the larvae immediately drink water before going dormant until May. When the bog violets flower in May, the larvae begin feeding on them exclusively into July. They then form a chrysalis and metamorphize into adult butterflies, living for about 45 days to lay their eggs in September.
The Service completed a comprehensive, peer-reviewed SSA to gather the best scientific and commercial data available and evaluated the threats to this subspecies. More information about SSAs can be found here and the SSA report for the silverspot is available today. As summarized in the SSA report, climatic conditions are expected to change across the range of the silverspot butterfly over the next 30 years, such that the viability of the subspecies may decrease in the future. Primary threats facing the silverspot butterfly include habitat loss and fragmentation, climate change, incompatible livestock grazing, human alteration of natural hydrology, and genetic isolation. The Service is not proposing critical habitat for this species due to the threat of collection and trade.
In addition, the Service is proposing an accompanying 4(d) rule, which would support tailored conservation of the species with balanced land management to allow continued acceptable land uses. The rule states that incidental take from the following activities would be exempt if they are done in a manner compatible with conserving the silverspot butterfly and bog violet: livestock grazing, haying or mowing, prescribed burning, brush control, noxious weed control, fence or structural maintenance.