If you own a dog in Spain, the pine processionary caterpillar (Thaumetopoea pityocampa) is one of the most serious seasonal dangers you will face. A single mouthful can cause severe tissue damage — and it can be fatal. This guide explains what they are, when the risk peaks, the warning signs, exactly what to do in an emergency, and how pet insurance covers the vet bill.
The pine processionary caterpillar (Thaumetopoea pityocampa) is the larva of a night-flying moth and one of the most significant forest pests across the Mediterranean. In Spain it is found throughout the mainland and the Balearic Islands, wherever there are pine trees — which, on the costas and in the countryside, is almost everywhere. It also affects cedars, and favours common species such as Aleppo pine, maritime pine and stone pine.
The caterpillars build distinctive white, cotton-wool-like nests high in pine trees over winter. What makes them dangerous is not a bite or a sting but their urticating hairs — tiny barbed hairs, present from the third larval stage onwards, that carry a toxin (thaumetopoein). When the caterpillar is threatened or disturbed, these hairs are released and can float in the air, causing irritation to skin, eyes and airways in people and animals alike.
They get their name from their most recognisable behaviour: when the time comes to leave the tree, they descend and move across the ground nose-to-tail in a long line — a “procession” — to find soft soil in which to bury and pupate. It is at ground level, during this procession, that dogs are most likely to encounter them.
Species and distribution information: Generalitat Valenciana — Procesionaria del pino fact sheet and the Junta de Andalucía species file.
The dangerous period — when the caterpillars leave the trees and are within reach of dogs at ground level — traditionally runs from late winter into spring, roughly February to May. However, this is shifting. Warmer winters have pushed the procession earlier in recent years, with caterpillars coming down as early as January in milder areas and along the coast.
Because the timing depends on temperature, it varies year to year and region to region — the mild Mediterranean costas often see them earlier than cooler inland or northern areas. The practical takeaway for dog owners is simple: from the turn of the year through late spring, treat any pine woodland, park or roadside with pines as a potential hazard, and be especially alert on warm, sunny days after cold spells, which often trigger a procession.
Because the caterpillar depends on pine trees, the risk closely follows where pines grow — and in Spain, that is almost everywhere. The species is found throughout mainland Spain and the Balearic Islands, from coastal pine forests to urban parks and the ornamental pines that line so many streets, urbanisations and golf courses.
For expats, that means the popular coastal areas are firmly in the risk zone: the pine-covered hills behind the Costa Blanca, Costa del Sol and Costa Cálida, the woodlands of Mallorca and the pine areas of the Canary Islands all host processionary caterpillars. Inland and mountain pine forests are affected too. The warmer Mediterranean coast tends to see the caterpillars descend earlier in the year than cooler inland or northern regions. Wherever you are, the rule is the same: if there are pines nearby, assume the risk is present in season.
Dogs are naturally curious and investigate with their nose and mouth — which is exactly what makes this caterpillar so dangerous to them. A dog that sniffs, licks or tries to eat a caterpillar (or even mouths ground contaminated by the shed hairs) comes into direct contact with the toxin on the most vulnerable tissue: the tongue, lips, gums and throat.
The reaction is fast and severe. The toxin causes intense inflammation and, in serious cases, necrosis — the death of tissue. The tongue can swell dramatically, turn dark or blue-black, and parts of it can be lost. Beyond the obvious impact on a dog’s ability to eat and drink, swelling in the mouth and throat can obstruct the airway and become life-threatening. If the dog swallows hairs, the damage can extend to the digestive tract.
This is why every dog owner in Spain needs to know the signs and act immediately. The first 30 minutes after contact are critical, and the difference between a full recovery and permanent damage — or worse — often comes down to how quickly the dog reaches a vet.
Symptoms usually appear very quickly after contact — sometimes within minutes. Watch for:
If you see any of these signs — particularly heavy drooling and a swollen or discoloured tongue — assume processionary contact and treat it as an emergency, especially in season and if your dog has been near pines.
Speed matters more than almost anything else. If you suspect contact, act immediately and get to a vet. Veterinary guidance generally advises the following steps:
At the clinic, vets act quickly to control the reaction and limit tissue damage. Treatment commonly involves thoroughly cleaning the mouth, anti-inflammatory medication, corticosteroids (such as dexamethasone) to bring down the swelling fast, antihistamines, and pain relief. Severe cases may need intravenous fluids, respiratory support, and hospitalisation for monitoring, and any dead tissue may require further treatment.
Because it is an emergency — often out of hours — and can involve hospitalisation and follow-up care, the cost can add up quickly. Exact fees vary by clinic and by how serious the case is, so we won’t quote a figure here, but an emergency visit plus treatment and any hospitalisation is not cheap. This is precisely the kind of sudden, unavoidable vet bill that pet insurance is designed to cover.
The severity of a reaction depends on how much contact the dog had, how quickly it was treated, and the individual animal. Mild cases — caught and rinsed fast — may recover well with prompt veterinary care. More serious cases can leave lasting damage.
Where the toxin causes necrosis, parts of the tongue can die and be lost, which can permanently affect how a dog eats, drinks and regulates its temperature. Dogs can also be left with breathing or swallowing difficulties, and the most severe cases can be fatal despite treatment. This is why the speed of your response matters so much: getting to a vet within minutes rather than hours can be the difference between a full recovery and permanent harm. It is also why avoidance during the season is the single most important thing you can do.
The best protection is avoidance during the season. Practical steps:
Prevention is far better than cure with this hazard, because even a fast response can’t always undo the damage a bad reaction causes.
The white, candy-floss-like nests in pine trees are where the caterpillars live over winter before descending. If you have pines on your property, those nests are a direct risk to your pets and family once the caterpillars come down.
Do not try to remove a nest yourself by knocking it down or burning it — disturbing it releases a cloud of urticating hairs that can cause serious irritation to your eyes, skin and airways. Nest removal and treatment (including trunk banding traps and, where appropriate, professional treatments) should be handled by a licensed pest-control company, ideally before the caterpillars leave the tree. Local councils sometimes treat pines in public areas, but private gardens are the owner’s responsibility.
Yes. Cats can suffer the same kind of reaction as dogs if they investigate a caterpillar, though free-roaming cats tend to encounter them less often than dogs on walks. The symptoms and the need for emergency treatment are the same, and cat owners in pine areas should be just as alert. Our cat insurance guide explains how cover works for felines.
For humans, the urticating hairs cause skin rashes, itching, eye irritation and, in some people, respiratory symptoms and allergic reactions. Children are particularly at risk because they may touch the caterpillars out of curiosity. Never handle them, keep children away from processions and nests, and seek medical advice if there is a significant reaction — especially any eye contact or breathing difficulty.
Processionary caterpillars are the most notorious seasonal hazard, but they are not the only one expat dog owners should know about. Spain’s climate and wildlife bring several risks that are less common in cooler northern countries:
All of these can lead to sudden vet bills, and several — such as leishmaniasis management or an emergency after a snake bite — can be expensive and ongoing. It is another reason so many owners in Spain take out pet insurance rather than face these costs out of pocket.
Processionary caterpillars are just one of the reasons vet bills in Spain can arrive without warning — alongside accidents, snake and insect bites, heatstroke in summer, and illnesses that need specialist care. Emergency and out-of-hours veterinary treatment is skilled work, and it is not cheap.
A pet insurance policy turns an unpredictable, potentially large bill into a manageable monthly premium, and means that in a genuine emergency your decisions are driven by what’s best for your pet, not by the cost. Cover typically reimburses a percentage of eligible costs up to an annual limit, includes free choice of vet, and covers you across Spain. Read our full guides to pet insurance in Spain, dog insurance and cat insurance.
An emergency like a processionary reaction is exactly what cover is for. Tell us about your pet and an English-speaking adviser will find a plan that reimburses your vet bills.
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