The pine processionary caterpillar (Thaumetopoea pityocampa) is known as ‘procesionaria del pino’ in Spanish and during late winter/early spring they come out of the trees and form conspicuous snakelike lines as they traverse the ground searching for soft soil to burrow into. In the adult phase they are a simple and unremarkable, short lived moth which emerges in the summer and flies at night.
These social caterpillars, living in family communities of up to 300 caterpillars per nest, eat pine needles by night and sleep in little temporary silk nests by day.
The caterpillars are covered in tiny barbed hairs which are their defence mechanism. These hairs are often being shed and so can be airborne around infested pine trees, on the branches where they have travelled and also left in the line of the migrating procession.
When humans and our pets come into contact with these hairs, they can cause reactions ranging from mild inflammation and irritation to severe anaphylactic shock. The worst problems occur if you make contact with the caterpillar directly and ingest the hairs, either by picking it up, stepping on it or moving them in some manner. Once on your skin a rash soon forms which can be incredibly itchy. Medical advice should be sought if you are unfortunate enough to experience this. The rash can be painful, very itchy and lasts for as much as three weeks.