Nests of the Pine Processionary Caterpillar (Thaumetopoea pityocampa) in pine trees in the Sierra Nevada mountains of southern Spain. These moth caterpillars attack and eat the pine needles, damaging the trees. They are responding to climate change by surviving at ever higher altitudes in the mountains as temperatures rise, allowing them to damage more trees. These caterpillars have a very effective defence mechanism. They are covered in thousands of tiny poisonous hairs called Trichomes. If handled these minute hairs cause irritation. They even release these trichomes into the air if the nest is approached.