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Black hairstreak (Satyrium pruni )

One of the rarest butterflies in the UK and the rarest hairstreak, the black hairstreak is beautiful but elusive. Adults live short lives and often rest high in tree canopies, making them hard to spot.

  • Not to be confused with the white letter hairstreak, the black hairstreak has a distinct row of black dots on their underwings.

    Credit: Tim Melling / Alamy

  • The black hairstreak's pupa camouflages cleverly as bird droppings.

    Credit: Gianpiero Ferrari / Alamy

Quick facts

Common name: black hairstreak

Scientific name: Satyrium pruni

Family: Lycaenidae

Habitat: woodlands, scrub and hedgerows in the East Midlands

Predators: birds and other animals

Origin: native

What do black hairstreaks look like?

Caterpillars: their appearance changes as they mature but they always blend perfectly with the plant they feed on. Early on, they look like blackthorn buds but as they grow, they develop a fresh green colouration to blend in with emerging shoots. Fully grown larvae have a pearly white head and a green body with rose-coloured markings. 

Pupa: they camouflage cleverly as bird droppings and remain in this stage for about three weeks before emerging as adults. 

Adults: underwings are brown with red edges, featuring a row of black spots, a white streak and small tails. Upperwings are brown with red edges. 

Wingspan: 34–40mm.

What do black hairstreaks eat?

Caterpillars: primarily blackthorn but occasionally wild plum and other Prunus species. 

Adults: honeydew secreted by aphids.

How do black hairstreaks breed?

Black hairstreaks breed in dense, mature blackthorn stands along wood edges, rides, glades or hedgerows. Smaller colonies breed in shady canopy gaps in mature woodland, scrub patches or sheltered hedgerows. Courtship involves the male and female whirling around each other for a few minutes before mating.

Females lay single eggs in forks of small blackthorn twigs, usually on rough patches, in June or July. The larvae spend winter inside the egg, partially developing and then pausing until spring. 

Black hairstreaks breed in dense, mature blackthorn stands, laying eggs in June or July.

Credit: Our Wild Life Photography / Alamy

Where do black hairstreaks live?

Black hairstreak colonies tend to stay within a single woodland area. Adults mostly spend their time in tree canopies or dense scrub where they feed on honeydew secreted by aphids. They're only found in the East Midlands, mostly in woodlands or hedgerows where there's blackthorn or wild plum. 

Did you know?

The black hairstreak butterfly was first discovered in 1828 in Cambridgeshire. At first, it was mistaken for the white letter hairstreak until an entomologist realised it was a completely distinct species and named it the black hairstreak. 

Signs and spotting tips 

They’re extremely difficult to spot due to their short lives, flying for about three weeks, and preference for high tree canopies. Occasionally, they come down to feed on nectar, but their fast, erratic flight makes them hard to follow.

In flight, they can be confused with white letter hairstreaks, so careful identification is important. The best time to see them is during the last three weeks of June.

Black hairstreaks prefer high tree canopies but you can spot them when they come down to feed on nectar.

Credit: Robin Chittenden / Alamy

Threats and conservation

During the 20th century, the black hairstreak declined steadily. The species is currently categorised as endangered on the GB Red List (2022) and is protected under Schedule 5 of the Wildlife and Countryside Act (for sale only). 

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