Compare with: purple hairstreak

White-letter hairstreak Strymondia w-album

Best time to see: Jul to early Aug

Key facts

A dark hairstreak butterfly with a white line like a W across its wings, usually in the treetops

Habitat: around large elm trees or bushes, such as along hedgerows or woodland edges

Once widely distributed through Wales and England, but suffering badly by the widespread loss of elms through disease


Dark brown underwings with a thin white line across each shaped like a W; orange crescents near edge of hindwing; 36mm

Usually perch high in a treetop, basking and drinking honeydew from aphids; occasionally make a rapid jerky flight out and back

Sometimes descend to feed on flowers


Females lay grey disc-like eggs on the sunny side of the canopy of elms on warm still days in late summer

Clear green slug-shaped caterpillars hatch in spring and feed first on elm flowers and later leaves

They pupate in June, emerging as adults from July onwards

© Ken Wooldridge