A Dog’s Cautionary Tail: Pine Processionary Caterpillars
Learn why Spanish Pine Processionary Caterpillars are dangerous to dogs, children, and adults. Symptoms, precautions, emergency actions, and safe removal tips
Introduction to Pine Processionary Caterpillar
Residents and visitors to Spain need to be aware of the Pine Processionary Caterpillar (Thaumetopoea pityocampa), known in Spanish as the Oruga Procesionaria de Pino, especially if you take pets for walks in parks near cities, go hiking with children and pets, or are near or underneath pine trees, which often line the beaches of Spain.
These caterpillars are covered with stinging hairs that can cause mild to severe allergic reactions when they come into contact with human or animal skin. This makes them harmful to young children and adults and potentially fatal to dogs and cats.
In this article I explain what Pine Processionary Caterpillars are, symptoms of a sting, how to avoid them, and the precautions you should take when out in nature in Spain.
What are Pine Processionary Caterpillars
Pine Processionary Caterpillars are usually around three to four centimetres (about 2 inches) long, with warm yellow, orange, or brown colouring. Their bodies are covered in millions of hairs that function as tiny poisonous barbs for protection.
They hatch from eggs (normally in spring) laid in large spider‑web‑like nests that cling between the needle leaves of pine trees. These nests act as a base while the caterpillars forage on the pine tree until they are large enough to descend to the ground. Once on the ground, they form a chain — sometimes up to two metres/yards long — of caterpillars (hence the name “processionary”) to search for a suitable underground place to pupate.
Pine Processionary Caterpillars will nest in loose soil or under rocks, digging down to form cocoons where they mature into moths. Studies show that they travel long distances at night to feed on pine trees far from their nests, even in freezing temperatures. They also travel during daylight in long chains.
The mature moth emerges, usually in autumn, eventually flying back up into pine trees to lay eggs. Each moth can lay around 300 eggs in a sticky mass fastened to pine needles.
The pine processionary caterpillar has few natural predators, although some bird species will eat them. When populations grow unchecked, they can cause significant damage to pine forests by consuming large quantities of pine needles.
Habitat of the Processionary Caterpillars in Spain
- Processionary caterpillars can be found in pine forests or mixed forests that contain pine trees in Spain.
- Coastal (litoral) areas behind beaches and rocky coastline
- Golf courses where pine trees are present
- Lower slopes of mountains where pine forests are abundant
- Private and public gardens and parks with pine trees
Processionary caterpillars are most prolific in spring, although they can be found from December through March depending on temperature. They may also be seen in summer in some high‑mountain pine forests.
Why are Processionary Caterpillars so Dangerous?
It is when they are in caterpillar form and walking across the ground that they are most dangerous, because they are easily accessible to humans and pets.
The millions of hairs on the pine processionary caterpillar contain a protein called Thaumetopoein, which in small doses can cause a rash similar to a nettle sting. In more severe cases, it can cause intense skin reactions and inflammation. The hairs act like tiny darts that detach from the caterpillar and embed themselves in the victim.
For dogs (and cats), the toxic hairs can cause serious problems when they come into direct contact with the nose or tongue, and when hairs attach to the animal’s fur and are later ingested during grooming.
- Symptoms to look for in your dog (even if you did not see direct contact with the caterpillar):
- Hypersalivation: One of the first signs is excessive drooling that appears suddenly.
- Inflammation of the contact area: The tongue, lips, mouth, paws or legs may become red, swollen and painful.
- Excessive swallowing: Caused by irritation in the mouth and throat.
- Agitation and restlessness: Dogs may appear nervous or distressed due to discomfort.
- Changes in the tongue: The tongue may turn red, purple (cyanosis), or even black due to impaired blood flow.
- Difficulty closing the mouth: Severe swelling can prevent the dog from closing its mouth properly.
- Ranula: Swelling under the tongue caused by saliva accumulation due to irritation of the salivary glands.
- Difficulty breathing: Swelling in the mouth or throat can obstruct the airway — a medical emergency.
- Eye problems: Contact with the hairs can cause blepharitis (eyelid inflammation) or corneal ulcers.
- Vomiting: Ingestion may cause vomiting, gastrointestinal distress, hyperthermia, tachypnea, or even anaphylactic shock.
Importantly, the hairs remain poisonous even after the caterpillars are dead. Lines of crushed caterpillars on roads still pose a danger to humans and pets — do not step on them or allow your pet to sniff, lick, or eat them. The hairs can also be shed as the caterpillars move.
The potential danger of pine processionary caterpillars should not be underestimated.
Precautions & Protections Against Pine Processionary Caterpillars
When walking in parks and gardens within towns and cities, it is likely that the council will take action to eliminate the caterpillars — although you should never assume this is the case. In Barcelona, the council undertakes measures to control processionary caterpillars in city parks and gardens.
- Spring: Plastic collars around pine tree trunks prevent the caterpillars from descending to the ground to forage or pupate. These collars can be filled with water to drown the caterpillars.
- Spring and Summer: Sprays and gels applied directly to processionary caterpillars on the ground to kill them.
- Summer and Autumn: Light traps for moths. Extermination of the processionary moth and release of non‑harmful species.
- Summer: Digging around the base of pine trees to locate and destroy larvae, using disposable or washable protective clothing and goggles.
- Early August: Spraying trees with Bacillus thuringiensis, a biological treatment harmless to humans and pets but lethal to caterpillars by disrupting their digestion and preventing egg development.
- Precautions to take when walking in pine forests:
- Short leash: Keep your dog on a short leash or at heel. Stay alert for caterpillars and steer your dog or child away from them.
- Be vigilant for nests: Look for nests in trees — a strong indication that caterpillars will be on the trunks and ground.
- Paws and fur: Wash your dog’s paws when you return home to remove any processionary caterpillar hairs. Brush out fur to reduce the risk of grooming‑related ingestion.
- Shoes: If you step on caterpillars, the treads of your footwear will trap toxic hairs. Shoes brought into the home can contaminate your pet’s environment. Hose off footwear after walks or hikes.
- DO NOT: Stomp on caterpillars or crush them with rocks — this can release venomous hairs into the air, which can land on you, your children, or your pets.
- Education: Teach children not to touch processionary caterpillars.
- Awareness: Encourage children and fellow hikers to call out if they see processionary caterpillars so others with dogs or children can avoid them.
- Paths: Stay on marked hiking paths when walking in pine forests.
The only reliable way to protect your dog from pine processionary caterpillars is to avoid pine forests with nests from late December until summer — which, in many parts of Spain, is extremely difficult.
Actions Upon Processionary Caterpillars Contact
- Action to take if your pet comes into direct contact with processionry catapillars:
- Do not rub or touch the affected area: The stinging spines of the processionary caterpillar release toxins when handled. Avoid touching the area with your hands and never rub it.
- Clean the mouth and tongue: If your dog has had contact with the caterpillar in its mouth, you can try rinsing with warm or hot water, as heat helps deactivate the toxin.
- Prevent your dog from licking the affected area: Licking or biting the irritated area increases toxin exposure and worsens symptoms.
- Consult a veterinarian immediately: If you suspect contact with a processionary caterpillar, seek veterinary help right away. Describe the symptoms and circumstances so the vet can act quickly.
- Don't delay treatment: Speed is crucial. Vets may prescribe corticosteroids and antihistamines to reduce inflammation and counteract the toxin.
- Avoid self‑medication: Do not give your dog any medication without veterinary supervision. Treatments and dosages must be specific to the case.
- Observe your dog closely: After contact, monitor your dog for changes in behaviour, appetite, or worsening symptoms. If anything deteriorates, contact your vet again.
Action to take when a human comes into contact with processionary catapillars:
Humans can react in different ways. A mild rash may respond to antihistamine cream, but if swelling is severe, pain is intense, or breathing becomes difficult, seek medical attention immediately.
If a child touches a pine processionary caterpillar, go to a doctor straight away. If the child has touched their mouth with an affected hand or put a caterpillar in their mouth, call the emergency number (112) immediately so a professional can guide you while help arrives.
Emergencies for Your Pet
Search engine term: Veterinario de emergencia en Barcelona para tratamiento de Oruga Procesionaria de Pino
Every pet owner should keep an emergency list to hand, and I am sharing mine with you here. The links below also include veterinarian‑written advice about processionary caterpillars, which is worth reading, especially those that go hiking with their dog.
- Veterinary Clinics:
- Veterinaria del Mar 24h:
Carrer de Marina 69, 08005 Barcelona — +34 900 023 308 - Balmesvet 24h:
Carrer de Balmes 205, 08006 Barcelona — +34 931 173 173 - Hospital Veterinari Garbí 24h:
Carretera N-II, km 643, 08349 Cabrera de Mar (5 minutes from Mataró) — +34 937 591 570 - Vetvida 24h:
Carrer Arcadi Balaguer 89 Bis, Castelldefels — +34 931 747 801 - Hospital Veterinario Montigalà, Badalona 24h:
Passeig Olof Palme 12, 08917 Badalona — +34 934 653 434 - Medivet 24h:
Carrer de Cervera 6, 08500 Vic — +34 938 852 264 - Dr Patino Veterinary Hospital 24h:
Carrer del Cardenal Vidal i Barraquer 34, 43005 Tarragona — +34 977 235 779 - Hospital Veterinari de Lleida 24h:
Carrer Joc de la Bola 16, 25003 Lleida — +34 973 280 896 - Hospital Veterinari de Canis 24h:
Can Pau Birol 38, 17006 Girona — +34 972 218 668
Avinguda Lluís Pericot 17, 17003 Girona — +34 972 227 170 - Hospital Veterinari de Canis 24h:
Avenida Salvador Dalí 13, 17600 Figueres — +34 972 670 179 - TomVets (Mon–Fri 09:00–20:30):
Multiple locations — +34 613 031 871
Elimination From Home or Business
If you find a Processionary catapillar nest on your property, you should not attempt to remove it yourself. Contact a professional elimination company to ensure safe removal and prevent exposure to toxic hairs.