Butterfly

A male marbled white butterfly, Melanargia galathea (Lepidoptera: Nymphalidae). In females the pattern on the underside of the wings is brown and white, not black and white.  This is what the upper side of the male's wings look like (the females look the same):

Photos taken in the field below Chazey Wood, near Caversham, UK, on 2011-06-21.