59 or 58?

It's relatively easy to become 'expert' on UK butterflies. The country only has 57 species that breed here and 2 regular migrants (the Clouded yellow and the Painted lady). There may soon be one less species to identify, as Britain's unique sub-species of the Swallowtail, is on the verge (https://www.theguardian.com/environment/2022/jun/22/britains-largest-butterfly-at-risk-as-fungal-pathogens-kill-food-source). The Swallowtail is Britain's largest butterfly and breeds in 16 locations, mainly around the Norfolk Broads. The butterfly's caterpillars exclusively feed on Milk parsley, growing in these locations. Last year, 90% of these plants died from Milk parsley droop, a disease caused by a fungal infection. Worried conservationists are currently monitoring the health of Milk parsley!