Quick facts

Common name: purple hairstreak

Scientific name: Favonius quercus

Family: Lycaenidae

Habitat: oak woods

Caterpillar footplants: sessile and English oak, and occasionally non-native oaks

Predators: birds

Origin: native

What do purple hairstreaks look like?

Caterpillars: brown and chunky with a deeper brown line along its back and paler oblique line along each side. It is covered in hairs and camouflages itself well against brown tree buds.

Adults: males are completely purple above while females only have a purple marking on the forewing. The underside is silvery grey with an orange eyespot on the hindwing. Both sexes have a pale streak under their wings, and they usually have short tails on the ends of their wings which resemble antennae.

Wingspan: 3-4cm

What do purple hairstreak butterflies eat?

Caterpillars: the leaves and flower buds of English oak and sessile oak.

Adults: mainly honeydew (a sweet substance secreted by aphids feeding on tree leaves), but sometimes also nectar sources like bramble.

Did you know?

Caterpillars rest during the day, waking at night in order to feed.

Purple hairstreak caterpillar on a plant stalk

Credit: Papillo / Alamy Stock Photo

How do purple hairstreak butterflies breed?

Towards the end of summer, eggs which look like miniature sea urchins are laid at the base of plump oak buds. While the caterpillars develop within the egg quickly, they remain dormant over the winter. They hatch the following spring when the buds break, with the caterpillars burrowing into the flower buds to feed. They reach adulthood by July.

Where do purple hairstreak butterflies live?

The purple hairstreak relies entirely on the oak tree to survive, using it as a food source, home and place to lay eggs. It is mostly found in oak woods across southern England and Wales, with scattered colonies further north. Recently it has been extending its range, particularly in the midlands, south-west Scotland and urban areas like London.

Purple hairstreak on an oak leaf showing bright purple upper wing

Credit: Andy Sands / naturepl.com

Signs and spotting tips

Step out into your nearest oak wood on a warm July evening, and look skyward. They can be difficult to spot, but if you’re lucky, purple hairstreaks will be out to play. They tend to stay around the treetops, and love nothing more than a game of chase on a summer’s evening – whole colonies can hang out in a single oak.

Threats and conservation

The purple hairstreak is common and not threatened in the UK at present.