The Downy Emerald (Cordulia aenea) is the rarest species in Norfolk, found in only one location in North-East Norfolk. As this is on private property, no location can be given. If you would like to see this species, the best location is at the Moat Pond at Thursley Common in Surrey (SU901417).
It flies between late May till mid July, and is usually found around tree-lined pools, although it can be found feeding in woodland glades. They fly earlier and later than many species, and seem to tolerate cool, windy weather better than most. Mating and feeding take place in treetops near to the pond and the males only patrol the ponds for short periods (30mins) before zooming back to the treetops.