This is a large and spectacular butterfly. The males are bright and yellow tinged with green. The females are almost entirely pale green.
They are most likely to be spotted on sunny days in April and May when they are mating. However, their distribution is sparse, mainly confined to the Midlands and west, with a stronghold in the Burren.
They are absent from Northern Ireland. This is because the caterpillars only feed on the leaves of two species of small tree, common buckthorn and alder buckthorn. Both of them, alder buckthorn in particular, are rare trees with a very limited distribution. If they were planted a bit more widely this beautiful butterfly would probably be more common.
Brimstones hibernate as adult winged insects, usually in holly or ivy, and produce one brood a year. They feed on the nectar of wild and cultivated flowers, including primroses, dandelions and vetches in spring and purple loosestrife, knapweed, scabious and buddleia in summer.
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