Within the classification of living things, the order Lepidoptera contains butterflies and moths. Skippers are a separate group within the butterflies. I learned on BugGuide.net that you can usually tell the three groups apart by the ends of their antenna. Butterflies have club-shaped ends, skippers have scoop-like ends, and moths have antenna with various simple or complex ends. This close-up of a Long Dash Skipper shows the scoop-like ends of the antenna pretty clearly.