Processionary Caterpillars in Spain – The Essential Safety Guide for Dogs & Families (2026)

This guide could save your dog’s life. That is not an exaggeration.

The pine processionary caterpillar (Thaumetopoea pityocampa) is one of the most dangerous pests in Spain for dog owners and families with young children. Every year, dogs die from contact with these caterpillars. Children are hospitalised with severe allergic reactions. And most expats moving to Spain have never heard of them.

If you live anywhere near pine trees in Spain — and pine forests are everywhere, from coastal urbanisations to rural fincas — this is essential reading. The processionary caterpillar season runs roughly from January to April, with peak ground activity in February and March. Learn to recognise them, understand the danger, and know exactly what to do if contact occurs.

What Are Processionary Caterpillars?

The pine processionary caterpillar (Thaumetopoea pityocampa) is the larval stage of a moth that is native to Southern Europe and one of the most destructive pine tree pests in the Mediterranean. The name comes from their distinctive behaviour: when ready to pupate, the caterpillars descend from their tree nests and march across the ground in long, nose-to-tail processions — sometimes 20 or more in a single line.

Life Cycle

Understanding the life cycle tells you when to watch out and when to act:

Summer (July-August): Adult moths emerge from underground pupae, mate, and lay eggs in bands around pine needles. Each egg band contains 100-300 eggs.

Autumn (September-November): Eggs hatch. Young caterpillars begin feeding on pine needles and spinning the white silk nests that become visible in tree canopies. These nests — which look like white cotton-wool bags — are the first visible warning sign.

Winter (December-February): Caterpillars continue developing inside their silk nests, emerging at night to feed. They go through five larval instars (growth stages). It is from the third instar onwards (typically late November-December) that they develop the dangerous urticating hairs.

Late Winter-Spring (January-April): Mature caterpillars descend from trees in their characteristic single-file processions to find soil in which to pupate. This is the most dangerous period — caterpillars are on the ground where dogs walk, children play, and people garden.

Underground (April-July): Caterpillars pupate in the soil. Some pupae can remain dormant for up to several years before emerging as moths, which is why the problem persists even after tree treatment.

Why They Are Dangerous

The danger comes from urticating hairs — tiny, barbed, microscopic hairs that cover the caterpillars from their third instar onwards. Each caterpillar carries approximately 600,000 of these hairs, which are released when the caterpillar is disturbed, stressed, or simply moving.

The Hairs

These hairs are not just irritating — they are actively toxic. Each hair contains thaumetopoein, a protein that triggers a severe inflammatory and allergic response on contact with skin, eyes, or mucous membranes. The hairs are barbed, meaning they embed in tissue and continue to release toxin.

Critically, the hairs are airborne. You do not need to touch a caterpillar to be affected. Walking near a procession, disturbing an old nest, or even being downwind of caterpillars can expose you to drifting hairs. Old nests remain dangerous for months after the caterpillars have left — the shed hairs persist in the silk.

Reactions in Humans

• Skin: Intense itching, red rash, raised welts similar to a severe nettle sting. Can persist for days to weeks.
• Eyes: Severe conjunctivitis, redness, swelling, and in serious cases, damage to the cornea. Requires urgent medical attention.
• Inhalation: Difficulty breathing, throat swelling, wheezing. Can trigger asthma attacks or anaphylaxis in sensitised individuals.
• Ingestion (children): Swelling of the tongue and throat, vomiting, severe pain. Small children who pick up caterpillars and put their hands near their mouths are at particular risk.

Repeated exposure increases sensitivity. The first contact may produce a mild rash; subsequent contacts can trigger severe allergic reactions.

CRITICAL: Dog Safety

This is the section that matters most. Dogs are by far the most frequent and most severely affected victims of processionary caterpillars in Spain. The reason is simple: dogs sniff the ground. They investigate strange moving things with their noses and mouths. A single moment of curiosity near a caterpillar procession can be fatal.

What Happens When a Dog Contacts Processionary Caterpillars

When a dog sniffs, licks, or mouths a processionary caterpillar (or even walks through an area where their hairs have settled on the ground), the urticating hairs embed in the tongue, lips, gums, and palate. The thaumetopoein triggers an immediate and violent inflammatory response.

Within minutes:

• Excessive drooling, often thick and ropy
• Pawing at the mouth and face
• Swollen tongue — can swell to two or three times normal size
• Visible distress and agitation
• Vomiting

Within hours if untreated:

• Tongue necrosis — tissue death of the tongue caused by the intense inflammatory reaction and impaired blood supply. This is the signature injury and can result in partial or total loss of the tongue.
• Inability to eat or drink
• Severe swelling of the throat potentially obstructing the airway
• Anaphylactic shock in severe cases

Without emergency veterinary treatment, dogs can and do die from processionary caterpillar contact. Even with treatment, many dogs lose part of their tongue permanently, affecting their ability to eat and drink for life.

EMERGENCY: What to Do If Your Dog Contacts a Caterpillar

Do this immediately — every minute counts:

1. Do NOT let your dog rub its face or lick its paws. Restrain gently if needed.
2. Rinse the mouth with water immediately — use a bottle or hose, directing the flow from back to front so the dog doesn’t swallow the hairs. Flush for as long as the dog will tolerate. Warm water is better than cold if available, as it helps dissolve the thaumetopoein protein.
3. Do NOT rub or wipe the tongue or mouth. Rubbing drives the barbed hairs deeper into the tissue.
4. Drive to the nearest emergency vet clinic (clinica veterinaria de urgencias) immediately. Call ahead if possible so they can prepare antihistamines, corticosteroids, and IV fluids.
5. Note the time of contact. This helps the vet assess the likely progression.

What the vet will do: Administer high-dose corticosteroids (dexamethasone) and antihistamines to control the inflammatory response. IV fluids to maintain hydration. Pain management. In severe cases, surgical debridement of necrotic tongue tissue may be needed days later.

Prevention for dog owners:

• Learn to recognise processionary caterpillar nests and ground processions (see below)
• Keep dogs on leads in areas with pine trees during processionary season (January-April)
• Avoid walking under pine trees during this period, especially after warm sunny days when caterpillars descend
• Muzzle your dog during walks in high-risk areas if your dog is a scent-driven breed that investigates everything with its mouth
• Carry a bottle of water on every walk during season — for emergency mouth rinsing
• Know the location of your nearest emergency vet clinic

What to Do If a Child Touches a Caterpillar

Children are attracted to the strange sight of caterpillars marching in a line. Younger children may try to pick them up. Even older children may not understand the danger.

If skin contact occurs:

1. Wash the affected area gently with warm soapy water. Do not rub — this drives hairs deeper.
2. Use adhesive tape (packing tape or micropore tape) pressed gently onto the skin and peeled away to remove embedded hairs.
3. Apply antihistamine cream (available without prescription at Spanish pharmacies).
4. If the rash is severe or the child develops breathing difficulties, swelling of the face or throat, or seems to be having an allergic reaction, call 112 (Spain’s emergency number) immediately.

If eye contact occurs:

1. Rinse the eyes with clean water for at least 15 minutes.
2. Do not rub the eyes.
3. Go to the nearest urgencias (A&E) — eye exposure to processionary hairs requires professional assessment to prevent corneal damage.

If ingested or if hairs are inhaled:

1. Call 112 immediately.
2. Monitor breathing closely.
3. Do not induce vomiting.

Season Timing by Region

The processionary season varies across Spain depending on altitude, latitude, and local microclimate.

Southern Coastal Areas (Costa del Sol, Costa Tropical, Costa de Almeria)

Nests visible from October. Caterpillars descend from December/January. Ground processions peak in January-February. Season largely over by March.

Mediterranean Coast (Costa Blanca, Costa Brava, Balearic Islands)

Nests visible from November. Descents begin in January/February. Peak ground activity in February-March. Season ends by April.

Inland and Higher Altitude (Sierra Nevada, Sierra Blanca, Madrid region, central plateau)

Nests visible from November-December. Descents delayed to February-March by cooler temperatures. Peak ground activity in March-April. Season can extend into May at higher elevations.

The Canary Islands

The pine processionary moth is also present in the Canary Islands, where the local subspecies (T. pityocampa in some references, or the closely related T. pinivora) affects Canarian pines. Season timing is variable due to microclimatic differences across the islands.

Identification: What to Look For

Silk Nests in Pine Trees

The white silk nests are the earliest warning sign. They look like dense white cotton-wool or candy-floss bags, typically 15-30cm across, situated in the canopy of pine trees, often on the sunny (south-facing) side of the crown. They’re most visible from late autumn through early spring.

Any species of pine tree can be affected: Aleppo pine (Pinus halepensis), maritime pine (Pinus pinaster), Scots pine (Pinus sylvestris), and Canarian pine (Pinus canariensis) are all hosts. Cedar trees (Cedrus spp.) can also be affected.

Ground Processions

The diagnostic sign: a single-file line of hairy caterpillars moving across the ground, nose-to-tail. Processions can be a few caterpillars to 30+ in length. The caterpillars are 30-40mm long, dark with reddish-brown hairs on their backs, and move slowly but purposefully toward softer ground for pupation.

Warning: Do not touch, disturb, or attempt to sweep away a procession. The caterpillars release their hairs when stressed, creating an airborne hazard. Keep people and animals well away — at least 3-5 metres — and report the location.

Where They’re Worst

Processionary caterpillars are found wherever pine trees grow in Spain, which is effectively the entire country. However, some areas experience consistently severe infestations:

• Urbanisations with mature pine trees: Many Spanish coastal urbanisations were built amongst existing pine forests. Developments across the Costa del Sol, Costa Blanca, and Balearic Islands are heavily affected.
• Sierra Blanca and Sierra de las Nieves (Malaga): Dense pine forests with large caterpillar populations.
• Sierra Nevada (Granada): High altitude extends the season later into spring.
• Interior pine forests: Castilla-La Mancha, Castilla y Leon, and Aragon all have significant populations.
• Rural and semi-rural properties (fincas, cortijos): Properties surrounded by pine forests experience the highest exposure.

If you’re buying or renting a property in Spain, checking for pine trees on and around the property is an essential part of your pest assessment. During the warmer months when processionary season ends, mosquitoes take over as the primary outdoor concern in many of the same areas.

Tree Treatment and Prevention

If you have pine trees on your property, proactive treatment significantly reduces the risk.

Btk Spray (Autumn Application)

Bacillus thuringiensis kurstaki (Btk) is a biological insecticide applied to pine tree canopies in early autumn (September-October) when caterpillars are in their early instars and still actively feeding on needles. Btk is ingested by the caterpillars and kills them within a few days. It is harmless to humans, pets, and most other insects.

Application: Requires spraying the entire canopy, which for mature pine trees means professional equipment — either a high-pressure sprayer or, for larger trees, a specialist tree treatment company. Cost: €30-80 per tree depending on size and accessibility.

Timing is critical: Btk must be applied while caterpillars are in their first or second instar (September-October). Later applications are less effective as older caterpillars feed less and are more resistant.

Pheromone Traps (Summer)

Pheromone traps hung in pine trees during June-August attract and capture adult male moths before they can mate, reducing egg-laying. They don’t eliminate the problem but can significantly reduce the following year’s population when used consistently.

Cost: €10-20 per trap, available from garden centres and Amazon.es. Use one trap per 1-3 trees.

Eco-Trap Bands (Trampa de Anillo)

Trap bands — also known as collar traps or eco-traps — are physical barriers wrapped around pine tree trunks that intercept caterpillars as they descend in their processions. The caterpillars enter a collection bag via a funnel and cannot escape.

When to install: November-December, before descents begin. Leave in place through April.

Cost: €25-60 per tree for commercial trap band kits, available from specialist suppliers and Amazon.es. Brands include Procerex and Ecopiège.

Advantages: No chemicals, physically removes caterpillars from the cycle, reusable.

Nest Removal

Physical removal of silk nests from trees eliminates the caterpillars before they descend. This is a job for professionals with appropriate PPE (protective clothing, respiratory protection, eye protection) and tree-climbing or elevated platform access.

Cost: €50-150 per tree, depending on the number of nests and tree height. Your local ayuntamiento may provide this service for trees on public land.

Warning: Never attempt to remove processionary caterpillar nests yourself without full protective equipment. The hairs are released in large quantities when nests are disturbed.

Spanish Municipal Responsibility

Under Spanish law, municipal governments (ayuntamientos) are responsible for pest control on public land and public trees. If processionary caterpillars are present on pine trees in public parks, along roads, in school grounds, or on municipal land, the ayuntamiento is responsible for treatment.

How to Report

Contact your ayuntamiento’s departamento de medio ambiente, parques y jardines, or sanidad. Most accept reports by phone, email, or through the local citizen reporting app (many municipalities now use the Linea Verde platform or similar).

Provide the exact location (street address or GPS coordinates) and describe what you’ve seen — nests in trees, ground processions, or both.

On Private Land

Treatment of processionary caterpillars on private property is the owner’s responsibility. However, if caterpillars from untreated private trees are posing a public health risk (e.g., processions crossing public paths or near schools), the ayuntamiento can order the property owner to treat their trees.

For properties in comunidades de propietarios (owners’ associations), tree treatment costs are typically borne by the community. Raise the issue at your community meeting (junta de propietarios) — this is a health and safety matter that should be budgeted annually.

Frequently Asked Questions

Final Thoughts

Processionary caterpillars are one of those uniquely Mediterranean hazards that catches expats completely off guard. They look innocuous — a curious line of fuzzy caterpillars on the ground — but they’re genuinely dangerous, especially for dogs. Together with wasps and scorpions, they form a trio of outdoor pests in Spain that can cause real medical harm.

The key takeaway: learn to recognise them, respect the danger, and know the emergency protocol. If you have pine trees on your property, budget for annual autumn treatment. If you walk your dog near pine trees between January and April, carry water for emergency mouth rinsing and keep your dog on a lead. Teach your children never to touch caterpillars of any kind.

This is one pest problem where prevention and awareness are infinitely more valuable than any treatment after the fact.

Related Guides

• Complete Cockroach Guide for Spain — the pest every expat deals with year-round
• First Year Expat Pest Guide — what to expect when you move to Spain
• Pest Control Safe for Pets — keeping your animals safe
• Emergency Pest Guide — immediate steps for any pest emergency
• Find a Professional — locate pest control providers near you