Pine processionary

The Greek physician Dioscorides noted the urtication caused by the pine-dwelling pityokampē caterpillar, the name meaning "Aleppo pine larva" (Ancient Greek: πιτυοκάμπη; from πίτυς pitys "pine" and κάμπη kampē "caterpillar"),[2] 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.[3]

The French entomologist Jean-Henri Fabre conducted a famous[4] 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.[5] 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.[4] 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 as 12 hours even when free on a flat surface.[4][6]

The adult is a stout furry moth which holds its wings like a tent over the body, in the manner of the eggar moths (Lasiocampidae). The adult is larger than the oak processionary, Thaumetopoea processionea, has a crescent marking on the wings (unlike the pale eggar moth; the oak processionary has an indistinct marking), and is found in coniferous rather than broad-leaved forests. The caterpillars are readily recognised by their processionary habit and their presence (with large silken nests and signs of defoliation) in coniferous woods. They are orange-brown and hairy with blue bands.[7][8][9]

The species is native to the southern Mediterranean area, North Africa, the Middle East, and southern Europe. It has been spreading northwards since the 1990s, assisted by climate change and by commercial activities including planting of host trees and transportation, and has reached Brittany, forests to the north of Paris, and Strasbourg in northern France.[7]

A paler subspecies, T. pityocampa orana, occurs in North Africa from Morocco to Libya, at altitudes to 2,000 metres (6,600 ft) in the Middle Atlas; the adults fly between April and August.[10]

Eggs on pine

Though most individuals of the species only live one year, some in high altitudes or more northern areas may survive for over two years. Each female lays an "enormous number"[7] of eggs near the tops of pine trees. After hatching, the larvae eat pine needles while progressing through five stages of development (instars). To survive through the winter, the caterpillars construct a nest of silk threads, making them one of the few species of temperate zone insects where the larvae develop in winter. Around the beginning of April, the caterpillars leave the nests in the procession for which the species is known. They burrow underground, pupate, and emerge between mid May and August.[7]

The eggs are laid in cylindrical bodies ranging from 4 to 5 centimetres (1.6 to 2.0 in) in length. The eggs are covered with scales which come from the female and mimic pine shoots.[7]

Adult

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.[8][11]

The moth's pupal stage occurs in a white silken cocoon under soil. The pupae measure around 20 millimetres (0.79 in) and are a pale brownish-yellow that changes into a dark reddish brown.[7][11]

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 millimetres (1.4 to 1.9 in), compared to a male's 31 to 39 millimetres (1.2 to 1.5 in).[7] Adults only live for a single day, when they mate and lay eggs. Males are able to fly several tens of kilometres, but the moth's dispersal depends on how far the female is able to fly during her short time as an adult. Her average flying distance is 1.7 kilometres (1.1 mi), with a maximum recorded of 10.5 kilometres (6.5 mi).[8][12]

The species is controlled to some extent by predators, parasites and viruses which attack the moth at many stages of its life cycle.[11] For example, eggs are eaten by the orthopteran Ephippiger ephippiger, while larvae are eaten by birds such as great tit (Parus major) and great spotted cuckoo (Clamator glandarius). Larvae are parasitised by solitary wasps (Ichneumonidae, Braconidae) and some species of flies (Tachinidae), and may be infected by the processionary moth virus Smithiavirus pityocampae. Pupae are eaten by hoopoes (Upupa epops), while adults are eaten by bats.[11]

• Mantis religiosa eating caterpillar, Pyrenees
• 
  Calosoma sycophanta beetle eating caterpillar, Turkey

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• Wildlife in France: Pine processionary moth