The green dock beetle (Gastophysa viridula) is one of several beetles that have a shiny, metallic sheen. Although primarily green they can also show gold, bronze and brass colours depending on their age and the brightness of the daylight in which you see them. The legs in this species are also metallic green which may help in identification from similar species.
Small beetles, the males are around about 5mm in length and females slightly bigger, they have distinctively separate head, thorax and abdomen body parts. They are part of the grouping known as leaf beetles and for good reason; as their common name implies they are generally found on dock leaves and their larvae can only develop if feeding on docks. They can strip leaves bare in a fairly short time and one often sees dock leaves with just veins and no 'flesh'. Rhubarb is a member of the dock family and this species can be a pest if they get established. If you go to pick one off of a leaf it will instantly drop to the ground.This is quite a hardy insect
Read more: Green Dock Beetle; the metal reflector