The green hairstreak (Callophrys rubi) is a small butterfly in the family Lycaenidae

It has a wingspan reaching about 26–30 millimetres (1.0–1.2 in) in length. The overside of the wings is a uniform dull brown, with two paler patches on the male's forewings made up of scent scales. The underside is bright green, with a thin white line that is often reduced to a faint row of dots or even missing altogether. The iridescent green colour of the underside is a structural colour caused by the diffraction and interference of light by microscopic repeating structures forming a diffraction grating in the wing scales. Green hairstreaks can be found at the end of March, with their flight time usually lasting until the end of June, but they are sometimes seen in July and early August. They never rest with their wings open, to maintain their green camouflage. The males exhibit territorial behaviour.

This picture, taken in 2015, shows a green hairstreak near Aston Upthorpe, Oxfordshire, within the North Wessex Downs Area of Outstanding Natural Beauty in the United Kingdom.

Photograph credit: Charles J. Sharp