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The White-letter Hairstreak is a small, dark triangular butterfly. It gets its name from the white markings on its underside that look like a letter ‘w’.

The larvae feed on elm - particularly Wych and English elm - and they hatch out from around the beginning of March.

The adult butterflies can usually be seen from about the second week in June to around the beginning of August. They take nectar from plants such as bramble and creeping thistle but they also feed on the honeydew found on elm and the leaves of other neighbouring trees, like ash and field maple.

If , like me when I first took on the task of species champion for the White-letter Hairstreak, you find identifying elm trees difficult here are a few tips:

• in spring, the trees are covered in pale green seed discs

• the serrated leaves are rough to the touch (there is one less common species that has smooth leaves, just to confuse us) and are usually asymmetrical where the leaf joins its stalk.

• the tree trunk bark of mature trees is gnarled and cracked.

Spotting White-letter Hairstreak butterflies can be tricky unless you know where and when to look. In cities, where elm trees might be some metres away from potential nectar sources, the most likely way to find them is by scanning the upper branches of mature elm with binoculars. As the butterflies feed on honeydew or look for a mate, their distinctive triangular shape and bobbing, jerky flight make them easy to separate from any other insects that might also be buzzing around at the top of a tree.

Where nectar plants are plentiful, for example if ‘host’ elm trees are surrounded by banks of bramble or thistle, White-letter Hairstreak butterflies are more likely to be found feeding closer to the ground but rarely much below head height.

The butterflies are at their most active on sunny days between 10:00am and 12:30pm and again in the early evening.

It is thought that numbers of White-letter Hairstreak butterflies have declined in the UK since the onset of Dutch Elm Disease from around 1961 which destroyed many elm trees across the country. There are, however, pockets of elm across the country that have stayed largely disease-free and Sussex is lucky to have one such area within its borders. Due to an intensive programme by the local authority to stop the spread of Dutch Elm Disease, Brighton and Hove now has the largest concentration of mature elm trees remaining in Britain with around 17,000 trees across the city. Some are in parks, others line streets and yet more can be found in school grounds and private gardens. Preston Park in Brighton is an excellent place to look for elm. In particular, there are two ancient English elm trees at the north-western entrance to the park beside the London Road. These magnificent specimens are thought to be 400 years old and in 2007 I recorded sightings of White-letter Hairstreak butterflies fluttering around the upper branches of both of them.

For more detailed information on a nationwide recording project of White-letter Hairstreak butterflies please see www.w-album.hertsmiddx-butterflies.org.uk.

If you can help with recording numbers of White-letter Hairstreak butterflies anywhere throughout Sussex, please contact me at the email address below.

Caroline Clarke

White-letter Hairstreak Species Champion

Email: caroandkevsmiled@netscape.net

October 2007

Horseshoe Plantation, Beachy Head, 14/07/06, Mike Snelling

Pavilion Gardens, Brighton, 14/07/06, Adrian Thomas

Beachy Head, 08/07/06, Michael Blencowe