Pine Processionary

• GeneralThe caterpillars move in single file, and their stinging hairs are a serious danger to dogs and children.
• Its pupae can enter diapause and stay buried for one to four years: a biological insurance policy that guarantees the population's survival if a fire destroys the pine wood.
• The urticating hairs are barbed and carry not a conventional toxin but a heat-labile protein, thaumetopoein, which causes contact urticaria and in rare cases anaphylaxis.
• It is one of the very few insects at our latitudes that lives out in the open and stays active right through the winter.
• Its name comes from the procession: the caterpillars come down from the tree in single file, each touching the rear end of the one in front with its head, following a silk thread. Jean-Henri Fabre set them walking in a closed circle around the rim of a flowerpot and they kept going round for days.
• Its urticating hairs are the problem. Each caterpillar carries hundreds of thousands of tiny hairs loaded with thaumetopoein, which detach on the wind and cause hives, conjunctivitis and respiratory reactions in people and animals.
• For dogs they are especially dangerous: contact with the tongue can cause necrosis and the loss of part of it.
• There is no need to touch the caterpillar: the hairs float in the air and remain urticating in the empty nests and on the ground for months.
• Its range is shifting northwards and to higher altitudes with warming, and that advance is one of the best-documented biological indicators of climate change in Europe.
• The white silk nests in the crowns of the pines are visible from the road in winter and give the infestation away.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat & environment

Mediterranean pine woods and pine plantations

Size at birth

The eggs are laid in a golden collar around a pair of pine needles

Gestation / incubation

The eggs hatch 30-40 days after laying, between mid-September and mid-October

Litter / clutch size

Up to 300 eggs per female in a single clutch. One generation a year, with five larval stages

Sources consulted: Generalitat Valenciana - Servicio de Sanidad Forestal; Comunidad de Madrid; Gobierno de Aragón (Sanidad Forestal); Vega et al., Actas Dermo-Sifiliográficas 2011; Koppert; Junta de Andalucía

Best time: The silk nests are visible in winter; the descending processions, between February and April; the moths, in July and August