Lycaeides melissa has colonized both cultivated and feral alfalfa (Medicago sativa) throughout much of North America within the past 200 years. We investigated the quality of the novel host as a resource for juvenile development, and asked if the novel host is a preferred host for oviposition relative to a native host (Astragalus canadensis). We find that the novel host is a relatively poor resource: adults reared on M. sativa were roughly one-third the size of adults reared on the native host, A. canadensis. The native host, Astragalus canadensis, is the preferred host in choice experiments. However, L. melissa females are known to lay eggs on M. sativa in the field at our focal location, where both M. sativa and A. canadensis are present. We hypothesize that ecological factors, including nectar availability for adults, might influence the distribution of adults in the field and the oviposition behavior of females.