Processionary caterpillars and dogs: what to do and how fast
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
If your dog has licked, bitten or sniffed a processionary caterpillar (or a nest), act straight away: put on gloves if you have them, rinse the mouth and tongue with plenty of clean water, without rubbing, letting the water run out of the mouth, then call your vet immediately. For advice on the way, you can also call an animal poison helpline — in the US the ASPCA Animal Poison Control Center, (888) 426-4435 (a consultation fee may apply), in the UK Animal PoisonLine, 01202 509 000, in France the CNITV in Lyon, 04 78 87 10 40. It is a genuine emergency, but one that is treated well: the time between contact and the first rinse has a direct bearing on the risk of lasting damage to the tongue. Do not feed your dog and do not make it vomit.
Contents · 6 sections
Why processionary caterpillars are dangerous
The pine processionary (Thaumetopoea pityocampa) and the oak processionary (Thaumetopoea processionea) carry thousands of microscopic hairs that break off at the slightest touch and release a stinging protein. Dogs investigate nose and mouth first, so the tongue, lips and lining of the mouth take the highest dose. Rubbing breaks the hairs and releases more toxin, which is why the advice is to rinse without rubbing. The hairs stay irritant for a long time, including in empty nests and on the ground where a procession has passed.
What the largest study in dogs shows
A study by Pouzot-Nevoret and colleagues, published in 2017 in Toxicon, followed 109 dogs treated in the intensive care unit of VetAgro Sup in Lyon, France, between 2000 and 2016 (see the study). Its results give clear reference points:
- 86% of dogs (94 of 109) had tongue lesions, ranging from swelling to necrosis;
- 55% had general signs, mostly vomiting (48%);
- survival was 97%, with a short hospital stay;
- among the dogs followed up long term, 23 (37%) permanently lost part of the tongue, with no major effect on their quality of life.
The most useful finding for owners concerns how soon the mouth is first rinsed. The table below uses the study’s figures.
| Time from contact to first mouth rinse | Share of dogs | Tongue necrosis on arrival |
|---|---|---|
| Under 2 hours | 35% | 5% |
| 2 to 6 hours | 37% | 5% |
| Over 6 hours | 28% | 45% |
Beyond 6 hours, the risk of tongue necrosis on admission was about 14.6 times higher, and necrosis developing during the hospital stay affected 65% of these dogs, against 21% when rinsing had taken place within 2 hours. The authors conclude that the best results come when rinsing happens within 6 hours. A three-case report published by Bruchim and colleagues in 2005 in Toxicon, from Israel, involving a closely related species (Thaumetopoea wilkinsoni), describes the same course: a badly swollen tongue, then necrosis and loss of its tip 2 to 5 days after admission, with all three dogs recovering (see the study). Two staff members developed an itchy rash on their arms and neck: protect yourself too.
What to do in the first 30 minutes
- Move your dog away from the caterpillar or nest and keep it calm.
- Protect your hands (gloves, a plastic bag): the hairs sting people too.
- Rinse the mouth for a long time with clean water, with your dog’s head tilted down, without rubbing the tongue or gums.
- Call your vet and say you are on your way; do not wait for symptoms to appear.
- Avoid touching your eyes; wash your clothes and your dog’s collar afterwards.
Signs to recognise
- Sudden heavy drooling, pawing at the muzzle or rubbing it on the ground.
- A tongue and lips that swell and redden, then may turn purplish or whitish.
- Vomiting, restlessness; more rarely difficulty breathing, which is an absolute emergency.
- In the following days, part of the tongue may darken and fall away: veterinary follow-up is essential.
When and where to be careful
In winter, the pine processionary builds white silk nests at the tips of pine and cedar branches; the caterpillars then come down in single file to bury themselves in the soil, in late winter and spring, earlier in southern regions. That is when dogs meet them on the ground. The oak processionary is active rather in late spring and summer, with nests stuck to tree trunks. In both cases, abandoned nests remain dangerous. The pine species has been spreading northwards for decades, and the oak processionary is now also present in parts of the UK: not having seen one before does not mean you are safe.
- In season, keep your dog on a lead under pines and oaks, and avoid areas with visible nests.
- In your garden, have nests removed by a professional; traps fitted around the trunk catch the caterpillars as they come down.
- Teach a reliable “leave it”: it is the best protection against anything lying on the ground. Grass awns and foxtails are the other big seasonal danger on walks.
- More health and hygiene advice is gathered in our dog care and grooming section and on the dog hub.
Frequently asked questions
Can a dog die from a processionary caterpillar?
It is rare once the dog is treated: survival was 97% in the VetAgro Sup study of 109 dogs. The main risk is losing part of the tongue, which is more likely the later the first rinse.
Should I rinse the mouth with vinegar or baking soda?
No: plenty of clean water, without rubbing. The treatment itself (anti-inflammatories, care of the tongue) is for the vet.
My dog only sniffed a nest: is it serious?
Airborne hairs can reach the nose, eyes and mouth even without touching a caterpillar. Look inside the mouth, rinse if in doubt and call your vet to ask whether a visit is needed.
Can symptoms show up later?
The mouth usually reacts quickly, but tongue necrosis can appear several days later. That is why a vet check is still worthwhile even if your dog seems better.
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This guide is part of Planète Pets’s Dogs universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
