page_title: Large tortoiseshell
section_title: Biology
hierarchical_section_title: Large tortoiseshell / Biology
caption_attribution_description: Français&#160;: Chenille de grande tortue (Nymphalis polychloros) English: Nymphalis polychloros caterpillar
context_page_description: The large tortoiseshell or blackleg tortoiseshell is a butterfly of the family Nymphalidae.
context_section_description: The adult insect (imago) 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 (ova) in a continuous band around the upper twigs of elm (Ulmus spp.), sallow (Salix caprea and Salix viminalis), pear (Pyrus spp.), Malus, Sorbus, Crataegus, Populus, and Prunus spp. trees.
  The caterpillars (larvae) 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 (late 1970s) was owing 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 (cremaster) at its rear end, to pupate. The chrysalis (pupa) is greyish brown with a slight silvery sheen. The species is univoltine, i.e. there is only one generation per year, the imagines emerging in July and August seek out sources high in sugar on which to feed. Tree sap and fermenting fruit are particularly popular.
caption: Caterpillar
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