In Britain and Ireland the White Letter Hairstreak one of our most elusive woodland butterflies, because it spends so much of the time high up in treetops. Early morning and dusk are the best times to see them, when they come down from the treetops to take nectar from privet, brambles, nettles and occasionally other kinds of wildflowers.
The common name comes from the distinctive letter 'W formed by white lines on the underside of the hindwings. The wingspan is approximately 36mm, and the wings are always held closed when the butterfly is at rest. The uppersides of the wings are dark brown with a small orange spot in the bottom corner of the hindwing, and unlike the female the male has a small pale spot, made up of scent scales, on its forewings.
Found throughout England and Wales, the White Letter Hairtreak becomes increasingly scarce towards the border with Scotland. This butterfly is found on mainland Europe and in parts of Asia, but it has not been recorded in North America.
This species has just a single brood. The eggs, which are laid individually on elm trees (Ulmus spp.) in summer are shaped like a flattened sphere with a central dome (a 'flying saucer' shape!). The caterpillars remain inside the eggs until the following spring, when they emerge and immediately burrow into and feed upon a flower bud. The loss of Elm trees due to Dutch Elm Diseae has, of course, had a serious effect on the populations of this lovely butterfly. Pupation, in April and early May, lasts about ten days.
This page includes pictures kindly contributed by the Countryside Council for Wales.
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