Nokomis Fritillary or Great Basin Silverspot
Caterpillars of this subspecies of Nokomis fritillary rely on bog violets as their main food source.
About This Species
The Great Basin silverspot was officially listed as threatened in February 2024. Today, there are 10 known populations made up of 21 colonies, subgroups that forage and breed within a smaller geographic area than the larger population. At least five colonies have been extirpated (died out) in the last 40 years.
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Physical Characteristics
The Great Basin silverspot has a wingspan of 2.5-3 inches. The undersides of the wings are orangish-brown with silver spots. For males the upper sides of the wings are orange with black markings (similar to many other fritillary species). In females, the upper sides of the wings are a dark bluish-black near the base, transitioning to a bluish-white color near the margins.
Range
This subspecies is found in western Colorado, eastern Utah, and northern New Mexico and Arizona.
Habitat
The Great Basin silverspot requires wet meadow habitats with an abundance of bog violets.
Diet
Great Basin silverspot caterpillars feed on bog violets, including northern bog violet, common blue violet and Le Conte’s violet. Adults drink nectar from a diversity of flowers, but primarily plants in the daisy family (Asteraceae).
Reproduction
The Great Basin silverspot typically lays its eggs in mid-September on or near its host plant, the bog violet. Before they develop into adults, caterpillars go through multiple stages of growth, called instar stages. Each instar stage is separated by a molt, when the caterpillar sheds its exoskeleton. The eggs hatch in early October and overwinter as a first-instar caterpillar. The caterpillars re-emerge the following May once the bog violets have reestablished. They feed on bog violets until about mid-July, when they form a chrysalis, a hard outer coating in which they develop into an adult butterfly. They break out of the chrysalis as adults in August. Adults live about 45 days, during which they drink nectar and mate. Females then lay eggs to start the cycle anew.
Threats to Species
The Great Basin silverspot relies on environments with snowpack, layers of snow in mountainous areas that don’t melt until spring or summer. Snowpack provides the moisture needed to sustain populations of bog violets, the host plant of Great Basin silverspot caterpillars; caterpillars also depend on snow packed habitats for spots that are cold enough to hibernate in. Climate change can keep snowpack from accumulating in winter, leaving caterpillars with less habitat. Genetic isolation is another threat to the Great Basin silverspot, as the 10 populations that exist are so far apart that there is little to no genetic mixing. This puts each population at risk of low genetic diversity, which can limit the population’s ability to adapt to environmental changes. Finally, habitat fragmentation (breaks in a habitat that prevent an animal from traveling to different parts of that habitat) is a major threat to this subspecies.