The butterfly ranges in color from white to pale yellow-brown, with red and black markings that indicate to predators it is unpalatable.

[3] Parnassius smintheus primarily feeds on the leaves of the Sedum lanceolatum plant as larvae and on its nectar as adults.

[5] 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.

[4] This includes the mountainous areas of Yukon, Alaska, and British Columbia in Canada, and as far south as New Mexico in the United States.

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.

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.

[4] The primary larval host plant is Sedum lanceolatum, spearleaf stonecrop, a yellow-flowered perennial succulent common in rocky habitats in Western North America.

[7] 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.

Consequently, the larvae often hurry to feed, then switch to another host plant within the time window offering the highest nutritional quality.

This suggests that in this species, the plug's primary role is to prevent the female butterfly from mating multiple times.

Females tend to search for good-quality meadows that have S. lanceolatum, though high host plant density is not required.

[14] The eggs are generally laid on the underside of flower heads, leaves, sticks, stones, moss, clumps of dirt, and sometimes on the larval foodplant.

The embryo develops into first instar larva within a month of oviposition but the egg does not hatch until the snow melts the next spring.

Conspicuous yellow markings appear on the body after the second instar, warning off predators, as the larva stores higher levels of sarmentosin.

They tend to feed rapidly on their larval host plant, then move to a basking location on open ground up to a few meters away for thermoregulation.

[3] If disturbed, the larvae twitch violently, then drop to the ground to seek cover, and may discharge a bad-smelling brown chemical.

[10] Adults are generally translucent yellowish white with black, grey, and red markings, though they vary greatly in color.

The population on Dividend Mountain near Penticton, British Columbia, is about half the size that habitat is capable of supporting due to cattle that graze the area after oviposition has occurred.

Birds are the most important predators of larvae and adult butterflies, as well as small mammals such as mice, chipmunks, and squirrels.

The closely related P. apollo also sequesters sarmentosin, but the concentrations were found to be nearly three times higher in P. smintheus adults.

[15] As a result of sequestering the compound, the butterflies have a strong odor and excrete brown fluid from their anus that smells like their body when attacked.

[3] The flight period spans the first week of June in low elevations to late September in alpine tundra.

Females of this species generally avoid flying, preferring to search for oviposition sites by crawling, whereas males more readily take flight.

Due to fire suppression and possibly global warming, the tree line has risen while the meadow areas have decreased by over 78% since 1952.

Short term warm weather in November could cause premature hatching of the eggs, the larvae of which would then die as normal winter temperatures resume.