Finding that Norfolk butterfly has been distinct subspecies for 200,000 years could transform conservation approach 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 c