British swallowtail split from European cousins much earlier than thought, study finds

The British swallowtail. Papilio machaon britannicus, is found nowhere else in Europe and is vulnerable to extinction. Photograph: Geoff du Feu/Alamy

The endangered swallowtail butterfly Papilio machaon britannicus, which is only regularly found breeding in Britain on the Norfolk Broads, has been a distinct subspecies for at least 200,000 years, according to a study.

Smaller, darker in colour and much rarer than the continental swallowtail, britannicus was previously considered to have developed its distinctive form during its confinement in the wetlands of eastern England over the last 8,000 years, after the flooding of Doggerland.