Britain’s largest butterfly at risk as fungal pathogens kill food source

Drastic die-back of milk parsley on Norfolk Broads threatens future of swallowtail

Britain's largest butterfly may be at risk from fungal pathogens that have caused a drastic die-back of the rare plant on which its caterpillars feed.

The swallowtail is only found breeding at 16 sites in Britain, all on the Norfolk Broads, where milk parsley grows. But last summer more than 90% of the milk parsley plants at one of its breeding sites wilted and died, preventing the plant from setting seed. If milk parsley disappears, the unique subspecies of the swallowtail found in Britain will become extinct.