Large Emerald Geometra papilionaria
Wingspan 40-50 mm.
The largest of the 'emeralds', and one which is common throughout most of Britain.
It inhabits woods, heaths and moors, and flies at night in June and July, when it is easily attracted by light.
The caterpillar is brown at first, but after overwintering becomes green with brownish 'warts', and feeds mainly on birch (Betula).