Mormon Fritillary

The Mormon fritillary (Speyeria mormonia) belongs to the group known as “brush-footed butterflies”, which are named for their tiny forelegs, hairy and useless for walking. A non-migrant, the Mormon fritillary is found in the western mountains (usually at higher elevations) from Southern Alaska south to California and east to Nevada, Arizona and New Mexico.

The upperside of the Mormon fritillary is intricately patterned in orange and brown without black scales on the veins. The wing margins are finely edged in white then black, then lighter circles and dark arcs. The wing undersides are a lighter yellowish brown with silvered spots. The antennae end in large, rounded knobs.

In the fall the Mormon fritillary adult lays eggs singly near the caterpillar (larvae) host plants. The caterpillars hatch in the fall but do not begin to feed. Instead the caterpillars hibernate until spring at which time they feed on their host plants (violets, if available, or other plants if there are no violets) until pupating. The adults emerge late in the season (July or August) and fly late into the autumn before laying their eggs. Adults feed on the nectar of many different plants but are particularly attracted to rabbit brush and wild asters.

Research published in 2012 showed a correlation between early snowmelt in the Colorado Rockies and Mormon fritillary populations. Global warming may be one of the factors contributing to the snow melting early in the year. In the spring the warmer weather and melting snow signal the end of winter. Subsequent spring frosts kill the early-emerging flower buds and plants. As the caterpillars begin to feed they do not have as many host plants and are also subject to the killing frost. Therefore fewer caterpillars become adult butterflies. Because of the frosts there is also a decrease in the number of flowers and consequently less nectar is available to insects. Adult fritillaries that have less nectar lay fewer eggs. So not only does the early snowmelt result in fewer adults, but those adults lay fewer eggs resulting in population declines.

These Mormon fritillaries were photographed on rabbit brush along the shore of Eagle Lake (Lassen County CA).

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