The phrase "rare butterflies" refers to a small group of butterflies that are not often found or seen. They are unique and uncommon to come across. Full definition
Using a bit of research and lots of careful gardening, this man was able to help reestablish a population of rare butterflies in his backyard. (treehugger.com)
Deciding how often and when to use prescribed fire can be tricky, especially when managing for rare butterflies, University of Florida scientists say. (sciencedaily.com)
One of America's Rarest Butterflies Finally Receives Protection under the Endangered Species Act (xerces.org)