Rising temperatures across England are fueling an explosion in oak processionary moth caterpillars, which sport toxic hairs that can trigger allergic reactions in humans and animals. These caterpillars, native to southern Europe, have been spreading northward for two decades, with warm summers accelerating their range. Health officials warn of respiratory irritation, skin rashes, and eye problems from contact with their hair-like setae, though severe reactions remain rare. The insects pose little direct threat to oak trees themselves, but their rapid expansion has prompted public health campaigns urging people to report sightings and avoid direct contact.