As Harry Pavulaan noted in a previous post here, our local complex of Celastrina species is generally difficult if not impossible to diagnose in the field or from a photo when looking only at the underside of the wings — which is what you typically see from perched or puddling azures.
But when they take flight the differences are much more obvious, especially among males, and with practice the ID can often be teased out. Here’s his pictorial guide to the dorsal wings, taken in natural light, for six of our spring-flying azure species.
Top Row: (left) C. ladon, Spring Azure; (right) C. lucia, Northern Azure
Middle Row: (left) spring form C. neglecta; (right) C. serotina, Cherry Gall Azure
Bottom Row (left) C. idella, Holly Azure; (right) C. neglectamajor, Appalachian Azure