Pine processionary

The pine processionary (Thaumetopoea pityocampa) is a moth of the family Thaumetopoeidae. The species was first described by Michael Denis and Ignaz Schiffermüller in 1775. Sometimes placed in the genus Traumatocampa, it is one of the most destructive species to pines and cedars in Central Asia, North Africa and the countries of southern Europe. The urticating hairs of the caterpillar larvae cause harmful reactions in humans and other mammals. 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 by their severely irritating hairs, as described by the French entomologist Jean-Henri Fabre. Though most pine processionary moths only live one year, some in high altitudes or more northern areas may survive for over two years. The adult moths lay their eggs near the tops of pine trees. After hatching, the larva eat pine needles while progressing through five stages of development. In order to maintain beneficial living conditions, silken nests are built over the winter. Around the beginning of April, the caterpillars leave the nests in the procession for which the species is known. They burrow underground and emerge at the end of summer. High numbers of adults are produced in years with a warm spring. The eggs are laid in cylindrical bodies ranging from 4 to 5 cm (1.6 to 2.0 in) in length. The eggs are covered with scales which come from the female and mimic pine shoots. The larva is a major forest pest, living communally in large 'tents', usually in pine trees but occasionally in cedar or larch, marching out at night in single file (hence the common name) to feed on the needles. There are often several such tents in a single tree. When they are ready to pupate, the larvae march in their usual fashion to the ground, where they disperse to pupate singly on or just below the surface. 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 rim of the pot. More recent studies, however, indicate that the caterpillars were actually physically trapped on the narrow rim of the pot, their feet unable to gain the secure purchase that would be needed to descend its steep, vertical walls. In one experiment, groups of processionary caterpillars of the same age as those observed by Fabre were placed on a flat table top and surrounded be a circular glass ring, 8 inches in diameter and 1 inch high. The caterpillars soon moved to the edge of the arena where they began to circle, one behind another. They were allowed to procession in this manner until they had a well established trail along the edge of the ring. The ring was then removed, freeing the caterpillars of any constraint to their activity other than their trail. The circular processions persisted for an average of just two minutes before the caterpillars marched off in a straight line. However, when circular trails were established in a similar manner by younger caterpillars they continued to circle for as long as 12 hours after the physical constraint was removed, a considerable time but far short to the seven days observed by Fabre. The moth's pupal stage occurs in a white silken cocoon under soil. The pupae measure around 20 mm and are a pale brownish-yellow color that changes into a dark reddish brown. As an adult, T. pityocampa has predominantly light brown forewings with brown markings. The moth's hindwings are white. Females have larger wingspans of 36 to 49 mm (1.4 to 1.9 in), compared to a male's 31 to 39 mm (1.2 to 1.5 in). Adults only live for a single day, when they mate and lay eggs. How far they are able to spread depends on how far the female is able to fly during her short time as an adult. Her average flying distance is 1.7 km (1.1 mi), with a maximum recorded of 10.5 km (6.5 mi). The species flies from May to July.