A 50-year dataset from the UK Butterfly Monitoring Scheme — the world's largest insect monitoring programme — shows that 33 of Britain's 58 native butterfly species have declined since 1976, even as warmer temperatures have helped others spread northward. While species such as the red admiral and comma have surged in number, habitat specialists like the pearl-bordered fritillary and white-letter hairstreak have fallen by 70% and 80% respectively, driven by habitat loss, nitrogen pollution, and indirect effects of climate change. Conservation efforts have delivered notable successes, including the large blue butterfly — declared extinct in Britain in 1979 and since reintroduced in Somerset — whose numbers have risen nearly 1,900%, but scientists warn that broader butterfly diversity continues to erode and that urgent habitat creation is needed.