Green Hairstreak

Sunny days from May to September are a good time to look for butterflies. The Green Hairstreak is one of my favourites. In Scotland, where I saw it last week, the Green Hairstreak is found in small colonies on moorland and on the edges of woods, where food plants such as Bilberry and Gorse grow.

The Green Hairstreak always closes it wings when it lands. In this position it cannot be mistaken for any other British species as the undersides of the wings are a beautiful almost metallic green colour. In spite of its bright colour the Green Hairstreak isn’t easy to spot among the new spring growth. And it has an almost supernatural ability to fly off just as you’re about to press the shutter on the camera. As with much of natural history photography time and patience is the key… Eventually the butterfly gets used to you and consents to have its picture taken.

Green Hairstreak butterfly photographed on 8th of May on the edge of deciduous woods near Struy, Inverness, Scotland.

Surprisingly little research has been done on the Green Hairstreak. Many details of its life cycle, colony structure and ecology are unknown. Like some other butterflies of this family the pupae have a relationship with ants. The pupae fall to the ground and produce a squeaking noise. Ants bury them in response, but the details of the process and the species of ant that are involved remains unknown.

Adult males and females look very similar. They are easiest to tell apart by their behaviour. Males are most commonly seen around shrubs and trees defending their territories from rivals. Females are more often found carefully searching for young flowers and leaves on which to lay their eggs.

An edge on view of a Green Hairstreak, the glancing incidence of the light here seems at first glance to rule out colouration produced by interference effects as seen in the previous post in the photo of the Purple Emperor butterfly. But note that the colour has changed subtly. Recent research shows that as with many other butterflies of this family colour is produced by structures in the scales rather than pigmentation.

The green colour of the Green Hairstreak is produced by light scattered and reflected from a strange mathematical surface known as a gyroid. Scales on the underwings contain gyroid structures oriented in different ways. The overall effect is to scatter green light in every direction… in a natural example of a photonic crystal. The light from the wings is polarised and since insect eyes are polarisation sensitive, it is thought that the light from them may produce an invisible signal of possible use in mating.

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