When I was out walking near Durham city with Allan Watson and Steve Ansdell this lunchtime Allan spotted a butterfly in the grass under an oak tree on the edge of some woodland, which turned out to be this exquisite male purple hairstreak.
You rarely see purple hairstreaks on the ground because they spend most of their lives in or around the crowns of oaks, so you need binoculars to watch them. This was an exceptionally lucky encounter. I suspect that it had just hatched from a pupa - it certainly looks in mint condition. Purple hairstreak caterpillars feed on oak foliage but they pupate underground in ants' nests, which is where this one would have emerged from.