Rare caddisfly thought extinct in Britain found in Wales

A caddisfly species thought extinct in Britain since 2016 has been found in north Wales, marking a notable rediscovery for freshwater biodiversity. Limnephilus pati was identified during a field survey at Cors Goch Nature Reserve on Anglesey, a finding that surprised researchers and highlights the value of ongoing monitoring of Britain's wetlands.

The insect has also been recorded at Market Weston Fen in Suffolk and on South Uist in Scotland's Outer Hebrides, making Anglesey one of only three places where the species persists in Britain. The distribution underscores the patchy nature of freshwater biodiversity across the country and the importance of protecting diverse wetland habitats where these rare insects can survive.

Caddisflies, of which there are about 200 species in the UK, look similar to moths and have hairy wings. They are an indicator group for clean water and healthy wetland ecosystems, because their larvae live underwater among dense vegetation. Adults emerge and fly at certain times of the year; in the case of Limnephilus pati, the adults fly from spring until early August, providing a seasonal window for researchers to study them in the wild.

The discovery occurred during a survey conducted by Natur am Byth, an NGO focused on saving threatened species in Wales, in collaboration with the RSPB and North Wales Wildlife Trust. Surveyors using light traps had been targeting the Limnephilus taricus species, but instead encountered Limnephilus pati, which is considered rarer and less well documented in Britain.

The habitats where these caddisflies are found are among the most diverse in Britain, including wetlands and waterways with ample vegetation. However, these environments are sensitive to drying out and to the impacts of agricultural intensification, pressures that scientists say can reduce water quality and disrupt the life cycles of aquatic invertebrates. Natural Resources Wales describes these habitats as at risk, even as they remain critical for supporting a range of wildlife.

Clare Sampson, Natur am Byth project manager for the RSPB, welcomed the find. She said, "It was a delight to find it at Cors Goch along with a number of other species that indicate clean water and a rich habitat," and added that "discoveries like this prove that there are always exciting finds in nature, and they can be found right on your doorstep." She also emphasized that consistent surveying is an important element of conservation work, noting that ongoing monitoring helps reveal hidden biodiversity and can guide protection efforts.

The discovery has practical implications for conservation planning in Wales and beyond. It demonstrates that even species long considered extinct in a region may persist in isolated refugia, and it reinforces the case for maintaining diverse, well-protected wetlands as a climate-adaptation strategy. As weather patterns shift and droughts become more frequent in parts of the UK, preserving habitats that support aquatic insects like Limnephilus pati is increasingly relevant to broader ecosystem health and resilience.