J.G., Newington.

Your photo shows a green grass dart, also known as the yellow-banded dart. It is one of a small group of skipper butterflies that rest with their wings in the distinctive “double-winged” stance shown. The front wings are held vertically, and the rear wings are held horizontally. The wingspan is only about 20mm.

This butterfly can be found in gardens where grass is green in summer and autumn. The introduced couch grass is a favourite food. It is a native insect whose caterpillars feed on both introduced and native grasses. Females are duller, with a greenish tint under the wings, so perhaps that is the origin of the unexpected name.