The Large Tortoiseshell Butterfly: A Remarkable Return and What It Means for UK Wildlife
After decades of absence, the large tortoiseshell butterfly (Nymphalis polychloros) is officially back as a resident species in the UK. Sightings in woodlands across Kent, Sussex, Hampshire, Dorset, Cornwall and the Isle of Wight have confirmed that this once-extinct butterfly is not only visiting, but breeding within Britain’s borders.
A History of Decline and the Role of Habitat Loss
The large tortoiseshell disappeared from the UK by the 1960s. Initial theories pointed to the devastating impact of Dutch elm disease, which decimated the elm trees that the butterfly’s caterpillars rely on for food. Yet, experts now believe the UK may have always been near the northern edge of the species’ natural range. This suggests that climate change is now playing a significant role in its return.
Climate Change and Butterfly Migration
Rising temperatures are enabling butterflies, and other insect species like the Clifden nonpareil moth, to expand their ranges northward. Increased numbers migrating from continental Europe, particularly from the Netherlands and France, have been observed in recent years. The warm summers of the 1940s saw a flourishing population, and similar conditions are now aiding its re-establishment.
Distinguishing the Large Tortoiseshell
It’s important to be able to identify this butterfly correctly. Unlike the more common little tortoiseshell (Aglais urticae), the large tortoiseshell is, as the name suggests, bigger. Crucially, it lacks the white patches found near the wingtips of its smaller counterpart.
Citizen Science and Monitoring the Population
Butterfly Conservation is actively monitoring the species’ progress and is urging the public to participate. Sightings can be logged on iRecord, a free citizen science app. This data is crucial for building a comprehensive picture of the butterfly’s distribution and tracking its expanding population. The charity has already added the species to its first sightings page.
Breeding Confirmed: A Positive Sign
Since 2020, evidence of large tortoiseshell caterpillars feeding on trees in the wild – initially in Dorset and now more widely – has confirmed that the butterfly is successfully breeding in the UK. The insect’s life cycle, which involves hibernation as an adult and egg-laying in spring, offers hope for a burgeoning population later in the year.
The Future of the Large Tortoiseshell
While the return of the large tortoiseshell is undoubtedly positive, experts caution that it’s not yet “back for good.” Richard Fox, head of science for Butterfly Conservation, emphasizes that the species isn’t yet widespread enough to be considered fully re-established. Continued monitoring and habitat preservation will be vital to ensure its long-term survival.
Frequently Asked Questions
Is the large tortoiseshell butterfly rare? Yes, it was considered extinct in the UK for many years and is still relatively uncommon.
What do large tortoiseshell caterpillars eat? They feed on the leaves of trees including elm, willow, aspen and poplar.
How can I help with butterfly conservation? You can log your sightings on iRecord, support Butterfly Conservation, and create butterfly-friendly habitats in your garden.
What is the difference between a large and small tortoiseshell butterfly? The large tortoiseshell is bigger and lacks the white patches found on the wings of the small tortoiseshell.
Did you know? The large tortoiseshell can hibernate as an adult, emerging in spring to mate and lay eggs.
Help us track the resurgence of this beautiful butterfly! Share your sightings on iRecord and contribute to vital conservation efforts.