Distribution
It is an extreme rarity in Britain, although it used to be widespread throughout England and Wales. Most of the specimens seen in Britain are thought to be captive-bred releases.
Reproduction
The adult insect over-winters in dry dark places, such as hollow trees or out buildings. In late February or early March the butterflies emerge and mate. The females lay their pale green eggs in a continuous band around the upper twigs of Elm, Sallow, Pear, and Prunus spp. trees.The caterpillars are gregarious, and systematically strip the topmost twigs of the tree bare. They seem to have little defence against predation by birds. It is possible that their decline and extinction in the British Isles was due to the loss of predatory birds, which previously had preyed upon smaller birds if they strayed to the tops of these trees.
The full grown larva spins a silk girdle around a twig further down the tree, and hangs from this by means of hooks at its rear end, to pupate. The chrysalis is greyish-brown with a slight silvery sheen. There is only one generation per year, and the imagos emerging in mid summer seek out sources high in sugar to feed. Tree sap and damaged ripe fruits are particularly suitable sources.
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