Brown Hairstreak

Thecla betulae

Very rare and restricted

Distribution and Status

The Brown Hairstreak has always been rare in our branch area. In the past, there were occasional reports of sightings in central Hertfordshire and Bricket Wood. Significant egg finds in Hampton, Richmond in December 2016 by Stephen Reisbach suggests possible expansion northwards from Surrey. Reports of eggs in Richmond and Hounslow in 2017-18 by Liz Goodyear and Andrew Middleton, and in Ickenham and Hayes by Paul Busby among others in 2018-19 seem to confirm the expansion. Adults were also seen in the Hillingdon area in 2018 and 2019. The occasional unconfirmed sightings in Hertfordshire in the last few years raise the possibility that there could be colonies elsewhere

Habitat Requirements

Woodlands and hedgerows containing blackthorn are required for this elusive butterfly to breed

Larval Foodplants

Blackthorn Prunus spinosa. Sometimes other Prunus ssp. are used

Adult Food Sources

Bramble Rubus fruticosis agg., Honey-dew, Thistles Cirsium sp., Common Fleabane Pulicaria dysenterica

Behaviour/Observation notes

The Brown Hairstreak is a very secretive butterfly and is therefore difficult to find so many organisations are now using egg-hunts to monitor populations as the white eggs are far easier to locate once it is known where they are likely to be. The females tend to stick to the same egg-laying sites year by year, selecting sunny and sheltered spots and usually lay eggs singly on blackthorn twigs of one or two years' growth in the early to mid afternoon. Males, on the other hand, hold territories high up in the tree canopy, usually around a tall ash tree. Because of the females' egg-laying and feeding habits, they are the easier sex to find and are more likely to be seen between around midday and 15:00 hours. Andrew Middleton and Liz Goodyear undertook some research on male territorial behaviour - see notes under Futher Information below

Life History

Male adults start emerging in late July but it is usually in the middle of August for females. The white eggs can be searched throughout the winter on the foodplant before they hatch in spring. The green larvae feed at night and rest on the underside of a leaf by day. When fully grown, they will descend to the ground to pupate

Further information

Notes on male territorial activity - Andrew Middleton and Liz Goodyear
UK distribution map
Full list of larval hostplants and adult food sources on Peter Hardy's database
Stevenage butterflies - additional notes