White-letter Hairstreak

The underwings are brown, with a white W-shaped streak, an orange edge and small tails. The Black Hairstreak is similar, but has a row of black spots on the hindwing. The White-letter Hairstreak has the erratic, spiralling flight typical of Hairstreaks.

It is difficult to spot, as it flies around the tops of trees, particularly Elms. It occasionally comes down to ground level to nectar on flowers, especially privet and bramble.

The species declined in the 1970s when its foodplants were reduced by Dutch Elm disease, but it is recovering in a few areas.

Size and Family

Family: Hairstreaks
Size: Small/Medium
Wing Span Range (male to female): 36mm

Conservation Status

Butterfly Conservation priority: High
Section 41 species of principal importance under the 2006 NERC Act in England
Listed on Section 7 of the Environment (Wales) Act 2016
UK BAP status: Priority Species
Protected under Schedule 5 of the 1981 Wildlife and Countryside Act (for sale only)
European threat status: Not threatened

Caterpillar Foodplants

The butterfly breeds on various elm species, including Wych Elm (Ulmus glabra), English Elm (U. procera) and Small-leaved Elm (U. minor). Research at one site has indicated a preference for (and a higher success rate on) Wych Elm. It breeds on mature trees, or abundant sucker growth near dead trees. It has also been shown to survive on the Dutch Elm Disease-resistant variety of U. japonica, Sapporo Autumn Gold.

Lifecycle

Habitat

The butterfly breeds where elms occur in sheltered hedgerows, mixed scrub and on the edges of woodland rides. The butterfly can also be found on large isolated elms.