Pine processionary caterpillar nest. Spun web nest (upper left) of the pine processionary caterpillar, the larva of the Thaumetopoea pityocampa moth, in a pine tree. These hairy caterpillars are found in forests in Spain, Italy, France, parts of northern Africa, and other Mediterranean areas. They live in communal webs and emerge during the evening and night to march in a single-file column (hence the name) to their food source. Their hairs can cause an allergic skin reaction if touched. Photographed in Andalucia, Spain.