Processionary caterpillar: some precautions to take in infested areas

The staff of the Alpi Cozie Parks has received several reports and requests from visitors concerned about the high presence of processionary caterpillars even within the protected areas managed by the Authority. This is an increasingly widespread problem due to dry and mild winters, which requires adaptation measures because fighting strategies have proven ineffective.
The Ministerial Decree of October 30, 2007, which made the fight against the processionary caterpillar mandatory, has been repealed by the Ministerial Decree of December 6, 2021. As a result, the management interventions for this issue are delegated to the municipalities where there are risks to human and domestic animal health.

What is the processionary caterpillar?

What we commonly call the processionary is the larva of a moth, the Thaumetopoea pityocampa. It is a small nocturnal moth whose caterpillars spend the winter in silk nests at the tips of pine branches (Pinus nigra and Pinus sylvestris) and more rarely in cedar, spruce, and larch. In the characteristic silky cocoons that resemble large cotton balls, the larvae grow protected, feeding on the needles of the host plant until the migration begins – or procession, hence the name – in a strict line on the ground where they burrow into the most suitable soil to pupate and complete their metamorphosis into butterflies.

The problems for humans and animals

The caterpillars at the final larval stage reach 3/4 cm in length, adopting black coloration on the head, gray on the back, and yellowish on the belly and are covered with microscopic stinging hairs that defend them from predators very effectively. Unfortunately, their filaments cause intense irritation to the skin and mucous membranes of humans and domestic animals, precisely at the moment when it is easiest to encounter them, that is during the migratory phase when they leave the crowns of the trees, traveling down the trunk to the ground. Climate change leading to increasingly dry and mild winters has favored the proliferation of the species and has advanced the maturation period of the larvae, which can often be seen in procession on the warmest days of December and January. Naturally, processionary caterpillars also severely damage the plants that host them by consuming their needles.

Precautions to be taken

• Avoid lingering near infested plants and/or areas.
• Avoid removing and/or touching nests with inappropriate means and methods and without adequate protection, as you may come into contact with the larvae possibly present inside.
• In infested areas, do not collect caterpillars or perform work that may spread stinging hairs into the air (raking leaves, mowing grass).
• Keep children and pets under control.
• For professionals in the sector, it is necessary to wear personal protective equipment (suit, goggles, gloves, and masks).

Is the processionary dangerous?

In humans, contact with the stinging hairs of the larvae can cause

• dermatitis;
• conjunctivitis;
• allergic inflammation of varying severity.

In domestic animals (dogs, cats, horses), an animal that comes into contact with the larvae may become nervous, swallow repeatedly, try to touch its mouth with its paws, and may present

• hypersalivation;
• tongue and facial edema;
• respiratory problems due to swelling of the laryngeal cartilages;
• vomiting if the larva is ingested;
• severe inflammatory reactions on the skin and mucous membranes;
• necrosis, particularly of the tongue.

What to do in case of contact?

In case of contact with the stinging hairs of the processionary caterpillar, it is advisable to

• take a shower promptly;
• change clothes on which stinging hairs may still be present (handling them with gloves);
• avoid scratching the affected areas to not increase itching and inflammation;
• wash contaminated clothing at least 60° (handling them with gloves);
• consider the use of topical anti-allergic remedies (creams and gels);
• visit a doctor or go to an emergency room.

In case of ingestion/inhalation of stinging hairs of the processionary caterpillar by dogs, horses, or other animals, it is necessary to intervene immediately by washing the areas that came into contact with a solution of water and baking soda (wearing latex gloves), to remove the stinging substance from the animal and inactivate the toxins.
Then take the animal immediately to the veterinarian where it will receive the specific care required.