Large Tortoiseshell Butterfly Confirmed as UK Resident After Decades of Absence
Rising temperatures across Europe have facilitated the remarkable return of the large tortoiseshell butterfly to southern England, marking its first confirmed residency in over six decades. This colourful and elusive insect, which vanished from British shores in the last century, has been officially reinstated as a native species following a series of early spring sightings.
Significant Sightings Across Southern Counties
Butterfly Conservation, the leading charity dedicated to insect preservation, has declared the large tortoiseshell (Nymphalis polychloros) a resident species in the United Kingdom. This announcement comes after individuals were observed emerging from hibernation in woodlands spanning Kent, Sussex, Hampshire, Dorset, Cornwall, and the Isle of Wight. These sightings have elevated Britain's list of native butterflies to sixty species, a positive development for biodiversity.
Richard Fox, head of science at Butterfly Conservation, expressed cautious optimism about the butterfly's return. "The signs are really positive, which is lovely," Fox remarked. "It is resident and therefore it is another species to add to Britain's total, which is good news. However, it's not well-established enough yet to say it's definitely back for good and will be widespread across multiple landscapes. We're still in that zone of uncertainty at the moment, but there are exciting signs."
Distinct Characteristics and Historical Context
Unlike the more common small tortoiseshell (Aglais urticae), which frequents gardens and feeds on nettles, the large tortoiseshell is a tree-dwelling butterfly. Its caterpillars primarily consume leaves from elm, willow, aspen, and poplar trees. The species is notably larger and lacks the white markings found on its smaller counterpart.
The extinction of the large tortoiseshell in the UK by the 1960s was once attributed to the loss of elms from Dutch elm disease. However, lepidopterists now believe that Britain may have always represented the northern limit of its natural range. The butterfly's resurgence is now being assisted by global heating, which has created more favourable conditions for its survival and migration.
Migration Patterns and Breeding Confirmation
The large tortoiseshell last flourished in Britain during a sequence of fine summers in the 1940s. In recent years, increasing numbers have migrated across the North Sea and the English Channel, driven by population surges in the Netherlands and France. Higher temperatures this century have also enabled many continental moth species, such as the spectacular Clifden nonpareil moth, to move into or re-establish themselves in Britain.
The butterfly first reappeared in significant numbers along the south coast in 2006-07, though many subsequent sightings were initially thought to result from unauthorised releases by butterfly breeders. Since 2020, however, large tortoiseshell caterpillars have been discovered feeding on trees in the wild, first in Dorset and now more widely. This confirms that the butterfly is breeding again in Britain, a crucial milestone for its resident status.
Lifecycle and Future Prospects
The insect hibernates as an adult, emerging in spring to mate and lay eggs. Its offspring take flight as adult butterflies in midsummer, raising hopes that this spring's sightings will lead to a burgeoning population later in the year. Butterfly Conservation has added the species to its first sightings page and is encouraging the public to log any observations on iRecord, a free citizen science app. This initiative helps build a comprehensive picture of the butterfly's distribution and expanding population across the country.
The return of the large tortoiseshell butterfly underscores the dynamic interplay between climate change and wildlife migration, offering a glimmer of hope for conservation efforts amidst broader environmental challenges.
