Processionary caterpillars: what to do in July 2026?

With climate change and milder springs, processionary caterpillars (Thaumetopoea pityocampa on pine, Thaumetopoea processionea on oak) are expanding their range across France and the Paris region. In July 2026, most property owners wrongly assume "the season is over": it is in fact a pivotal period to break the reproduction cycle before the August egg-laying.

Since the decree of 27 April 2022, the processionary caterpillar is classified as a health hazard. The owner of infested land is liable for any harm caused to a third party — neighbour, passer-by or pet.

Why July is a decisive month

The processionary cycle spans almost a full year. In July:

• Male moths emerge from their chrysalises and actively seek females;
• Fertilised females lay eggs from late July on pine needles or oak leaves;
• each laying releases 150 to 300 eggs that will become next year's stinging colonies.

It is therefore the ideal window to trap the males with pheromone traps and dramatically reduce next year's pressure. The earlier you act in July, the weaker the next season starts.

The real danger to humans and animals

Urticating hairs (microsetae) stay active for several months, including in empty nests, ground litter and shed skins. They cause:

• severe skin reactions (hives, erythema, swelling);
• eye disorders on contact;
• asthma attacks if inhaled;
• in dogs, a life-threatening risk if licked or swallowed: swollen tongue, necrosis, respiratory distress — absolute veterinary emergency.

Dog walking in a wooded park in summer, heightened vigilance against processionary caterpillars

The right 2026 strategy: what to do (and what to stop doing)

What to stop doing in July

• ❌ Manual nest removal on pine: too late — caterpillars have already descended in processions (January–May) or pupated in the soil.
• ❌ Burning a nest without protection: urticating hairs disperse in the air and worsen exposure.
• ❌ Over-the-counter insecticide spraying: useless on eggs, dangerous to other animals.

What to do by tree

| Tree | July 2026 action | Ideal period | |------|------------------|--------------| | Pine | Install pheromone traps right away | June – August | | Oak | HEPA vacuuming of nests + pheromones | May – August | | All | Watch for late ground processions | South: until June |

For oaks still holding nests, professional vacuuming with a cherry picker is the safest method. For pines, pheromone traps are the most cost-effective investment: a single trap catches hundreds of males and halts local reproduction.

Large oak tree in summer, host of the oak processionary

The pheromone trap: how to use it

1. Pick a species-specific trap (pheromone capsule "pityolure" for pine, "processionea" for oak).
2. Install the trap 2–3 m above ground, on the edge of the infested area, never inside the hotspot.
3. Replace the capsule every 4 to 6 weeks (June, July, August).
4. Empty the bucket regularly and dispose of catches (soapy water, sealed bag).
5. Combine with a BtK (Bacillus thuringiensis kurstaki) biological treatment from mid-August on young larvae.

When to call a ProDeratisation professional

A Certibiocide-certified pest control technician is strongly recommended if:

• the tree is over 4 to 5 metres tall or several trees are infested;
• you are in a sensitive area: school, nursery, public park, public-access building, immediate neighbourhood;
• you have children, dogs, cats or horses to protect;
• a nest is still visible and accessible in an oak.

Our technicians carry out a free on-site diagnosis, install pheromone traps, schedule follow-up visits and handle safe nest removal by vacuuming or pruning depending on the season. For a fast intervention in Île-de-France (Paris, Seine-et-Marne, Yvelines, Essonne, Val-de-Marne, Hauts-de-Seine, Seine-Saint-Denis, Val-d'Oise), contact us or request a quote online.

Protecting your dog: best practices

• Avoid wooded areas with pines and oaks between January and July (procession season).
• Keep dogs on a lead in parks and forests around Paris.
• Rinse thoroughly with cold water (never rub) muzzle and paws in case of suspected contact.
• Call a vet immediately in case of excessive drooling, tongue swelling or vomiting — every hour counts.
• Monitor winter nests (white silky "pouches") until destroyed.

Key takeaways for summer 2026

• ✅ July = pheromone window, not nest removal.
• ✅ The earlier you install, the lighter next season.
• ✅ Dog + processionary = immediate vet emergency.
• ✅ Infested land = legal liability for the owner.
• ✅ Professional = free diagnosis, safe intervention, annual contract available.

Do not let the season close without acting: fighting processionary caterpillars is a matter of timing. Request your processionary caterpillar diagnosis today.