Greenstreaks …
The Green Hairstreak is the most widespread of all the British hairstreaks. However, it is also a local species, forming colonies which can be as small as a few dozen individuals, although larger colonies exist. There is one brood each year, the butterfly typically being seen from mid-April to the end of June, depending on location.
The sexes look very similar and are most readily told apart in the field by their behaviour. Rival males may often be seen in flight whilst defending their territories. The less conspicuous females are more often encountered searching out nectar sources and foodplants on which to lay her eggs.
They always settle with their wings closed, the brown uppersides only ever being seen in flight. The undersides, by contrast, provide the illusion of being green, an effect produced by the diffraction of light on a lattice-like structure found within the wing scales, which provides excellent camouflage as the butterfly rests on a favourite perch.
More at:
www.ukbutterflies.co.uk/species.php?species=rubi [Accessed, 23rd April 2020].