Four species of blue and the closely-related brown argus occur in Norfolk. They are often as easily identified by habitat, behaviour and date as by their appearance. The holly blue may be ruled out by its plain silvery underwings and by the fact that it flies high among trees and shrubs. The chalkhill blue may be ruled out as in Norfolk it occurs at only one site, as its larval foodplant is extremely rare. Both the silver-studded blue and the brown argus may more easily be confused with the common blue. The former, like the common blue, has blue males and brown females but it is restricted to a few heaths and has only one adult generation which flies in high summer, essentially between the two generations of the common blue. A blue butterfly flying low over a wildflower meadow in early summer or late summer is very likely to be a common blue. A brown butterfly of the same size with orange spots along the edge of its wings might be a common blue female or a brown argus. The brown argus never has a blue wash to its body and the base of its wings.