The processionary caterpillars guide
Identification, risks, life cycle and prevention: answers to the most common questions about pine and oak processionary caterpillars.
Pine and oak processionary: two species to watch for
The pine processionary (Thaumetopoea pityocampa) builds a visible silky white cocoon in the branches, typically between autumn and winter. The oak processionary (Thaumetopoea processionea) is more discreet, forming nests at the base of the trunk or in low branches, and moves in the characteristic single-file line that gives the species its name. Our processionary caterpillar treatment handles both species.
A cycle tied to the seasons
Caterpillars hatch in late summer, develop inside their cocoon through autumn and winter, then descend to the ground between January and April to bury themselves and pupate into moths — this descent phase carries the highest risk of contact, especially for pets.
Dangerous urticating hairs
According to Anses, each processionary caterpillar carries several hundred thousand microscopic urticating hairs that detach at the slightest contact or air movement, causing skin, eye and respiratory irritation in humans. In dogs, contact or licking can cause tongue necrosis requiring emergency veterinary care. See the full Anses factsheet → Given the risk, don't take chances — call our certified, fully equipped team.
Acting before the risk period
Pruning the cocoons is best done in autumn or winter, before hatching, by a professional equipped to avoid any contact with urticating hairs even on a nest that looks inactive. Trapping collars fitted around the trunk before the spring descent intercept caterpillars without using any pesticide. Check out our processionary caterpillar treatment to plan an intervention that fits your schedule.
Frequently asked questions
Processionary caterpillars: the full FAQ
It's the larva of a moth that feeds on pine needles or oak leaves. It's covered in urticating hairs and moves in single file, hence its name.
The pine processionary builds a clearly visible white silky cocoon in the branches, while the oak processionary forms a more discreet nest directly on the trunk or main branches.
Their microscopic urticating hairs detach easily into the air and cause skin, eye and respiratory reactions, which can escalate to severe allergic reactions.
Yes, extremely: a dog that sniffs or licks a caterpillar can develop tongue necrosis within hours — an absolute veterinary emergency.
A whitish ball- or spindle-shaped cocoon hanging in a pine's branches, or a line of caterpillars moving in procession along an oak trunk, are the most visible signs.
Nests form in autumn and grow throughout winter. Caterpillars descend from the trees to bury themselves generally between January and April, the period of highest risk.
Without proper protective equipment, handling a nest releases a massive amount of urticating hairs into the air, with a high exposure risk for you and those around you.
A trapping collar is fitted around the trunk and intercepts caterpillars as they descend to the ground to bury themselves, guiding them into a collection bag, with no chemical product involved.
Traps releasing a pheromone attract and capture male moths before reproduction, reducing the number of nests formed the following season — a method that complements pruning.
Regularly checking pines and oaks in autumn, pruning nests preventively as soon as they appear, and fitting collars before the descent period greatly reduce the risk of reappearance.
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