Quick facts
Common name: Brown hairstreak
Scientific name: Thecla betulae
Family: Lycaenidae
Habitat: hedgerows, scrub, woodland edges
Caterpillar foodplants: blackthorn, bullace
Predators: birds
Origin: native
Brown hairstreak (Thecla betulae)
An elegant butterfly with a shy reputation, the brown hairstreak spends most of its time high in the tree tops, flitting around woodland edges and hedges in the late summer sunshine.
What do brown hairstreaks look like?
Caterpillars: bright green and hairy with pale white striped markings. They have dark brown heads that are often tucked underneath and so not visible.
Adults: have dark brown upperwings with a large orange patch on each forewing that is much larger and brighter in females than males. There is also a small amount of orange on the hindwing tails. The underwings are an orange brown with two wavy, white streaks.
Wingspan: 3.8–4cm.
What do brown hairstreaks eat?
Caterpillars: the leaves of blackthorn are preferred but related species such as bullace and other plum varieties are suitable.
Adults: mainly feed on aphid honeydew, though will also visit flowers for nectar.
Did you know?
Just before the mature caterpillar leaves its foodplant to pupate, it turns from bright green to a dull purple or lilac colour, helping to maintain camouflage in the undergrowth.
How do brown hairstreaks breed?
Breeding typically occurs high up in favoured ‘master’ trees within the colony, which are usually ash. Females lay their eggs singly on blackthorn leaves, often in sheltered locations, where the eggs then overwinter. Caterpillars emerge in the spring and feed until late June and July when pupation occurs. Butterflies appear on the wing through late summer and into autumn, making the brown hairstreak one of the latest-flying butterflies in the UK.
Where do brown hairstreaks live?
The brown hairstreak is mainly found in southern and central England and south-west Wales. The species favours habitat where blackthorn is abundant, usually in hedges, scrubby areas and woodland edges.
Did you know?
Due to its bright orange forewing markings, the female brown hairstreak was once thought to be a separate species known as the golden hairstreak.
Signs and spotting tips
This is a notoriously elusive species but ash trees along woodland edges are a good place to look as they flutter high amongst the branches. Closer to the ground, females are most likely to be seen as they disperse to lay eggs. Brown hairstreaks enjoy warm, sunny weather, and might be seen basking with wings open as they warm up.
Threats and conservation
Brown hairstreak numbers have declined significantly in the UK in recent decades, primarily due to the loss of hedgerows and the widespread practise of hedge flailing (trimming), which threatens overwintering eggs. It is now a priority species for conservation.
