Brown Hairstreak Species
30th January 2012
The largest hairstreak species in the UK, these are one of the latest of our butterfly species to emerge, with adults’ first taking flight in late July or early August. The same breeding sites are used year-on-year but despite this their presence can be difficult to determine. To spot them look upwards as males especially spend their time high up on a ‘master’ tree, often Ash, where adults engage in courtship and mating and feed on aphid honeydew. When the time comes to lay eggs in August, females can be spotted as they search for suitable young Blackthorn growth (the larval food plant) in sunny spots of hedgerows or on the edges of woodland. Eggs are laid singly in the forks of a blackthorn twig over large areas.
Latin name: Thecla betulae
Population Numbers: A rare species in southern England and Wales, in the UK the Brown Hairstreak is a conservation priority with an estimated 99% decline in numbers over 25 years (1980 – 2005). In Wiltshire it is confined to two discreet population areas one in the north and one south-east. While not considered to be threatened in mainland Europe, populations there are also suffering declines.
Where to see and when: At this time of year the tiny white eggs, said to resemble sea urchins in appearance, are much more apparent on bare branches, and so this is an ideal time to try and spot them.
Wiltshire Wildlife Trust is fortunate enough to have Brown Hairstreaks on a number of our northern reserves including Echo Lodge Meadows; Clattinger Farm; Ravensroost Meadows; Blakehill Farm; Distillery Meadows and Stoke Common Meadow.
At Distillery Meadows the habitat is reminiscent of years gone by when much of north Wiltshire was comprised of small family-run farms creating a patchwork of fields and hedgerows. These thick hedgerows include blackthorn and therefore provide ideal egg laying sites for the Brown Hairstreak.
Meanwhile at Stoke Common Meadows its uninterrupted role as hay meadows has made this site a haven for a wide range of wild flowers, the hedgerows has also remained largely untouched and with the presence of blackthorn is another site where Brown Hairstreak larva can feed and pupate undisturbed.
What’s being done: It is suspected that the Brown Hairstreak’s severe decline is largely link to unsympathetic farming practices which including the flailing of hedgerows containing overwintering eggs. Therefore hedgerow management practices on Wiltshire Wildlife Trust reserves’ work on a rotational basis ensuring that while necessary trimming or laying is carried out, some sections are left unmanaged to ensure that eggs are undisturbed. These sections will receive management in the following or future years.
A number of the Trust’s reserves are also sites for on-going monitoring of Brown Hairstreak egg numbers by Michael Sammes of Butterfly Conservation. If you would like to become involved in these surveys contact Michael at michael@sammes.co.uk
The Trust is also acting to increase suitable habitats for the Brown Hairstreak outside of our reserves by providing advice on hedgerow management to local landowners and farmers.
