This blue is well, showing off its blue, what the subfamily is named for. The Boisduval’s is a larger blue, approaching one and half inches and is on the wing in late spring into summer in a wide variety of habitats (mountain meadows, forest openings, prairies). The males are lilac-blue with dark borders on the upperside, while the females may be brown, or blue with wide dark borders. Females lay eggs on new growth of lupine species (Lupinus). Caterpillars feed first on leaves, then flowers and seedpods. The caterpillars also enter into a mutually beneficial relationship with ants. Caterpillars produce a sugary secretion which is eaten by the ants that protect them. This species sticks to the west, from British Columbia east to the western edge of the Great Plains, south to New Mexico, Arizona, southern California, and Baja California. 
Photo by Gage Poore on 6/28/20 in the Rattlesnake Recreation Area near Missoula, MT.