The largest butterfly in the United Kingdom is under threat. The Swallowtail can only be found at 16 sites, all of which are on the Norfolk Broads where a specific type of plant, the rare ‘Milk Parsley’ grows.
In the past, conservation efforts, including preventing water extraction, have been implemented to protect the rare plants and the creatures that thrive off of it.
The swallowtail is classified as “vulnerable” to extinction in Britain on the latest IUCN red list because it is restricted to the low-lying Norfolk Broads.
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.
The “milk parsley droop”, which may be caused by a known fungal pathogen combining in a novel way with another pathogen, was spotted near Norwich. Nature reserve managers across the Broads are now on high alert for signs of the disease spreading this year, with the wilt typically taking hold in July and August.
The butterfly is also under threat from the possible rise in sea levels which will result in the loss of some freshwater marshes that the swallowtail and its food plant currently inhabit.
Plant pathologists are urgently seeking to identify the cause of the droop. One line of enquiry is linked to a fungal pathogen identified in umbelliferous plants including commercial crops such as carrots.
The story of the threat to the Swallowtail is a sadly familiar one. 41% of species in the UK have declined since the 1970s and each year around two animals or plants become entirely extinct.