The pine processionary (Thaumetopoea pityocampa) is a moth of the subfamily Thaumetopoeinae in the family Notodontidae, known for the irritating hairs of its caterpillars, their processions, and the economic damage they cause in coniferous forests. The species was first described scientifically by Michael Denis and Ignaz Schiffermüller in 1775, though it was known to the ancients, with remedies described by Theophrastus, Dioscorides and Pliny the Elder. Its processionary behaviour was described in 1916 by the French entomologist Jean-Henri Fabre. It is one of the most destructive species to pines and cedars in Central Asia, North Africa and southern Europe. The species is notable for the behaviour of its caterpillars, which overwinter in tent-like nests high in pine trees, and which proceed through the woods in nose-to-tail columns, protected from predators by their severely irritating hairs. The species is one of the few insects where the larva develops in winter in temperate zones. Global warming is causing the species to affect forests progressively further north. The urticating hairs of the caterpillar larvae cause harmful (and in some cases allergic) reactions, in humans and other mammals. History of study The Greek physician Dioscorides noted the urtication caused by the pine-dwelling caterpillar, the name meaning "Aleppo pine larva" (; from pitys "pine" and kampē "caterpillar"), in his 77 AD book De materia medica. Pliny the Elder recorded a treatment for the resulting itching in his Natural History; Theophrastus had earlier recommended the medicinal plant elecampane (horse-heal) in oil and wine to treat contact with "pine larvae" in his Historia Plantarum. The French entomologist Jean-Henri Fabre conducted a famous study on the pine processionary caterpillar where a group of them followed head-to-tail in a circle around the rim of a flower pot; they continued marching in the circle for a week. He described the experiment in his 1916 book The Life of the Caterpillar. The study has been cited innumerable times by inspirational and religious speakers who view it as a metaphor for blindly following a leader or for confusing activity with accomplishment. Fabre considered his caterpillars to be mindless automatons, trapped because they were pre-programmed to blindly follow trails, in this case the endless one that they had laid down around the circular pot rim. Fabre's caterpillars may have been physically trapped on the narrow rim of the pot, but circular trails established by young caterpillars do continue to circle for as long