A variety of factors affect how much certain plants are eaten by herbivorous insects. In the eastern foothills of the Rocky Mountains of Alberta, Canada, Parnassius smintheus larvae have been described as virtually monophagous on Sedum lanceolatum, however a second host plant Rhodiola integrifolia is found in the region. We explore the differences in herbivory, larval performance, and oviposition between host plants. We also surveyed host plant abundance in the field to determine the amount of feeding damage on both species. In the lab, we found that there was no preference for feeding on S. lanceolatum versus R. integrifolia. The growth and survival of P. smintheus larvae also was not affected by the host plant. In the field we found much lower rates of herbivory on R. integrifolia than S. lanceolatum. We conclude that there are differences in herbivory observed in the field because P. smintheus larvae encounter R. integrifolia much less than S. lanceolatum. Possible mechanisms include the two host plants occurring in different microhabitats, P. smintheus females not ovipositing near R. integrifolia, or P. smintheus larvae not being able to detect R. integrifolia from a distance.