Parnassius smintheus

Parnassius smintheus, the Rocky Mountain parnassian or Rocky Mountain apollo, is a high-altitude butterfly found in the Rocky Mountains throughout the United States and Canada. It is a member of the snow Apollo genus (Parnassius) of the swallowtail family (Papilionidae). The butterfly ranges in color from white to pale yellow-brown, with red and black markings that indicate to predators it is unpalatable.

Parnassius smintheus primarily feeds on the leaves of the Sedum lanceolatum plant as larvae and on its nectar as adults. The butterfly tends to reside in meadows and avoids forests, because it strongly prefers light. The males of this species fly from meadow to meadow frequently to find females and food resources, whereas females are more likely to avoid flying. The males seem to have mate choice in this species, as they emerge from the pupae earlier than the females and patrol for females, heavily preferring newly emerged females that have not yet flown.

Although the species is not yet endangered, the climate change and human activity over the last few decades have reduced its viable habitats, and this process is continuing.

The range of the butterfly is based primarily in the Rocky Mountains, which spans Canada and the United States. This includes the mountainous areas of Yukon, Alaska, and British Columbia in Canada, and as far south as New Mexico in the United States.

P. smintheus can often be found in alpine and subalpine meadows. It was found that males of this species preferred meadows with a greater abundance of nectar flowers and a higher quantity of the host plant Sedum lanceolatum. They also preferred meadows with a greater number of females of their species. Males may sample two or more meadows to gain information on their relative quality. It has been suggested that this preference in males for meadows with more food resources may be due to their increased energy requirements, as they spend much more time flying than females. In contrast, the female butterflies showed no preference for meadows with more nectar flowers or host plants, or for greater numbers of males.

The primary larval host plant is Sedum lanceolatum, spearleaf stonecrop, a yellow-flowered perennial succulent common in rocky habitats in Western North America. Larval foodplants may less frequently include other stonecrop species, including S. divergens, S. oreganum, S. stenopetalum, and S. integrifolium. The foodplants tend to grow most abundantly on steep, well-drained, gravelly slopes. They can mostly be found 20–40 meters above the tree-line. Herbivores rarely feedon S. lanceolatum, because it produces a deterrent cyanoglycoside, sarmentosin, so there is little risk that larvae will be accidentally preyed upon as a result of the foodplant being ingested.

The larvae also sequester sarmentosin from the plant in their bodies for their own defense. However, it has been found that if the S. lanceolatum plant becomes physically damaged by mechanical means, the larvae feeding on it have reduced growth rates, possibly due to an induced defense by the plant itself. While damage by insects does not cause plant defense, damage from feeding by the larvae does induce defense by the plant. Consequently, the larvae often hurry to feed, then switch to another host plant within the time window offering the highest nutritional quality. Larvae will typically feed and leave a plant in less than half an hour. From November to February, the leaves of their foodplant are fatally toxic to the larvae, but for the rest of the year, the larvae feed and develop normally. If the snow melts before March, the eggs hatch while the larval foodplant is still toxic, and the larvae perish.

Males of this species often have poor visual discrimination, so they investigate all flying or sitting objects of the approximate size and color of the females of their species. They primarily identify females by their light color, so they are as likely to chase small blue lycaenids as they are to chase large white butterflies, but tend to ignore darker butterflies like fritillaries. The males emerge from their pupae before females do in order to patrol for newly emerged females over a large area. They patrol by flying over large areas then investigating any resting or flying females after spotting them. Males fly long distances continuously in search of females, stopping only to bask or feed.