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The important points, first
- From February to April, in areas with pine trees, watch for lines of caterpillars on the ground and fallen nests.
- Sudden drooling, a swollen tongue, pawing at the mouth or struggling to breathe after a walk need a veterinarian straight away.
- In a study of 109 dogs, tongue necrosis was much more common when the mouth was first rinsed more than 6 hours after contact.
- Do not scratch or rub your dog’s tongue, and do not touch caterpillars or nests with bare hands.
What it is and when it is most dangerous
The pine processionary moth (Thaumetopoea pityocampa) is one of the main pests of pine trees, especially in the Mediterranean region. The larvae live in a silk nest built high in the pines. At the start of spring, when temperatures rise slightly, they leave the nest in a line, “in procession”, and go down to the ground to pupate. The caterpillars’ hairs carry tiny structures that break when the caterpillar feels threatened and release an irritant toxin.
According to a veterinary review, dogs come into contact with the caterpillars mainly during processions, sometimes through a fallen nest or hairs carried by the wind. A Portuguese study describes dogs living near pine woods as frequently exposed. In Italy too, processionary caterpillars are among the animal toxins behind calls about pets to the Milan Poison Control Centre.325
Signs to recognise
The most common contact is with the mouth. The dog becomes nervous, swallows repeatedly, paws at its mouth and drools heavily. Within a few minutes the tongue swells and the mouth becomes inflamed. In severe cases the dog cannot close its mouth or struggles to breathe because the larynx swells. If it swallowed caterpillars it often vomits. After 2–5 days the tip of the tongue may become necrotic and slough off.
In a French study of 109 dogs, 86% had tongue lesions, from swelling to severe necrosis, and 55% had general signs, mostly vomiting (48%) and less often breathing difficulty (5%). The hairs can also get into the eyes. In a Spanish study of 140 dogs they mainly caused keratitis and uveitis, which almost always healed after the hairs were removed and the veterinarian treated the eyes.314
Why every hour counts
In the study of 109 dogs, tongue necrosis was already present on arrival in 45% of dogs whose mouth was first rinsed more than 6 hours after contact, compared with 5% of those treated earlier. These dogs also had a much higher risk of developing necrosis while in hospital. The best results came with rinsing within 6 hours, and overall survival was 97%.
In the Portuguese study of 41 dogs, all those arriving after more than 2 hours developed tongue necrosis, and the authors conclude that the veterinarian should intervene within 2 hours. Among dogs in the French study followed long term, more than one in three permanently lost part of the tongue, usually without major effects on quality of life.12
What to do and how to prevent it
Move your dog away from the caterpillars and leave for the veterinarian straight away, telling them it is a processionary caterpillar exposure. Do not scratch the tongue: the hairs break and release more toxin. Do not touch caterpillars or nests with bare hands, as people can react too. Treatment, from rinsing the mouth to medicines against inflammation, is for the veterinarian.
The veterinary review advises walking dogs in areas without pine trees, especially from February to April. Published cases involve dogs, but the authors consider close contact with the caterpillar dangerous for both people and animals: if your cat goes into a garden with pine trees and nests, keep an eye on it during those months.32
Sources and checks
Numbers in the text lead to the exact source. Commercial blogs and social posts are not used as evidence.
- 1Peer-reviewed research article
Pine processionary caterpillar Thaumetopoea pityocampa envenomation in 109 dogs: a retrospective study
Toxicon (2017) · PubMed PMID 28356233 · 109 dogs: tongue lesions in 86%, necrosis much more common when rinsed after 6 hours, 97% survival, permanent necrosis in 37% of dogs followed long term.
Link checked on 16 Sept 2026 - 2Peer-reviewed research article
Effects of pine processionary caterpillar Thaumetopoea pityocampa contact in dogs: 41 cases (2002–2006)
Zoonoses and Public Health (2012) · PubMed PMID 21824369 · 41 dogs: drooling, dysphagia, pain; tongue necrosis in all dogs arriving after 2 hours; dogs near pine woods often exposed; reactions also reported in people.
Link checked on 16 Sept 2026 - 3Peer-reviewed research article
Pine processionary caterpillar, Thaumetopoea pityocampa Denis and Schiffermüller, 1775 contact as a health risk for dogs
Annals of Parasitology (2015) · PubMed PMID 26568988 · Full text on the journal website: life cycle and early-spring processions, ways of contact, clinical signs, tongue not to be scratched, walks away from pines from February to April.
Link checked on 16 Sept 2026 - 4Peer-reviewed research article
Ocular lesions produced by pine processionary caterpillar setae (Thaumetopoea pityocampa) in dogs: a descriptive study
Veterinary Ophthalmology (2016) · PubMed PMID 26608091 · 140 dogs with hairs in the eyes: keratitis and uveitis, 99% healed with hair removal and treatment.
Link checked on 16 Sept 2026 - 5Peer-reviewed research article
Plants and zootoxins: toxico-epidemiological investigation in domestic animals
Toxicon (2021) · PubMed PMID 33798604 · Calls to the Milan Poison Control Centre 2015–2019: processionary caterpillars among the reported animal toxins.
Link checked on 16 Sept 2026
Contact with processionary caterpillars is a veterinary emergency. This guide does not replace an examination and does not recommend home treatments.