Hairstreaks are among the most special of butterflies, but not for any dazzling display of colour. In fact, the reverse is the case. They must be some of the plainest of Britain’s day-flying Lepidoptera. The most arresting feature is an orange slash along the hindwing, and if it’s a particularly fresh individual it can be studded with azure specks, from which depends the tiniest curving wing spur.
Nor are hairstreaks particularly rare. But they do live in a place that we seldom visit, or even look: in the trees way above our heads. Largely for this reason, white-letter and purple hairstreaks – and both are on the wing about now – are probably among the most widely distributed butterflies that people have never seen or even heard of.
The first of them takes its odd name from the white zigzag lines through its wing. It is the more restricted of the two and must have seriously declined in the last half-century because of a dependence on elm trees. The national nature reserve at Hay Dale is exceptional for retaining an avenue of about 30 mature wych elms. While many of the neighbours have been reduced to bare, beetle-riddled stumps, these surviving trees give a sense of what we had before so-called “Dutch” elm disease swept through these islands.
When I visited early during the 2020 lockdown, I remember enjoying the abundance of their pale lemony seedheads, and the rather brittle but densely emerald foliage, and also speculating whether the elms’ specialised dependents might also survive here. This week I had my answer.
For most of their short adult lives, white-letter hairstreaks keep to the canopy, feeding on honeydew produced by aphid colonies living in the same spot. If these supplies should fail, however, hairstreaks descend to ground level to seek alternative nourishment. The nectar from creeping thistles seems to be the food of choice.
And late afternoon from about 4pm-6pm appears to be the precise window they favour. By chance we visited this place at that moment. And there it was: delicate, subtle, beautiful and blessed, a tiny god of the treetops come to earth for gravity-bound mortals to cherish.
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