Processionary Caterpillar Alert Spain

March 2026 has brought one of the most active processionary caterpillar seasons in recent years across Spain. A mild winter — with overnight temperatures rarely dropping below 8°C in coastal areas — has allowed colonies to develop faster than usual, and the ground-descent phase is happening earlier and more intensively than many residents expect.

If you walk your dog anywhere near pine trees in Spain, this update is urgent reading.

What Is Happening Right Now?

The pine processionary caterpillar (Thaumetopoea pityocampa) spends winter in silk nests high in pine trees. When temperatures warm in late winter, the caterpillars descend to the ground in their characteristic single-file processions to pupate. This descending phase — February through April in most of Spain — is when the danger peaks, because the caterpillars release toxic hairs freely as they move across the ground.

In 2026, that descent is happening ahead of schedule and across a broader area than usual. Entomologists attribute this directly to warmer average winter temperatures linked to climate change — a pattern that has been intensifying for more than a decade. For a deeper look at how changing temperatures are affecting pest behaviour in Spain generally, see our guide on climate change and pests in Spain.

What Is Happening in Each Region?

Costa del Sol (Málaga Province)

The area around Marbella, Mijas, Torremolinos, and the Gibralfaro hills has been specifically flagged by experts from Andalucía’s Society of Entomology. They note that pine forests throughout Málaga province — including areas around Doñana National Park, Sierra de Grazalema, and the Aznalcázar area in Sevilla — are expected to see high caterpillar numbers through March.

Local councils are advising residents to check park paths before letting dogs off leads and to avoid allowing children to approach any caterpillar processions on the ground.

Balearic Islands

The Balearic Islands saw their processionary season begin in mid-February, earlier than typical. The Department of Agriculture and the Natural Environment deployed preventive treatments on over 2,400 pine trees across Palma’s city parks and green spaces last autumn, followed by active nest removal and incineration in February.

The municipality of Calvià has implemented sound cartridges — a precision method of nest destruction that avoids chemical treatment — across its parks. Ground-level caterpillar presence is still expected throughout March despite these preventive measures. Walkers in Son Vida, Es Capdellà, and forested areas around the island should stay alert.

Ibiza and Formentera

The Pitiüses islands are running an extensive campaign this year involving aerial application of Bacillus thuringiensis (Bt) over 15,000 hectares. Bt is a naturally occurring soil bacterium that kills caterpillar larvae but is non-toxic to mammals, birds, and beneficial insects. Ground support has also installed bat shelters and pheromone traps to reduce adult moth populations for next season.

Despite this intervention, ground-level caterpillars are still present and active in March. Hikers and dog walkers on forested paths near San Juan and the north of the island should exercise caution.

Madrid

Madrid completed its 2025–2026 municipal campaign with more than 53,500 processionary caterpillar nests removed from city parks and green areas. That figure is actually down from previous years — the City Council attributes this partly to favourable weather conditions and to the cumulative effect of several years of preventive treatment. However, the ground-descent phase is still underway in March in wooded parks including Casa de Campo and El Pardo.

Why Are Processionary Caterpillars Dangerous to Dogs?

Dogs are the most vulnerable group because they investigate through smell and touch — exactly the behaviours that trigger caterpillar hair release and ingestion. A dog that sniffs, licks, or bites a caterpillar can experience a medical emergency within minutes.

The caterpillars’ hairs cause rapid and severe inflammation wherever they make contact. In the mouth and tongue — the most common site of exposure in dogs — the result is intense swelling, necrosis of the tongue tissue, and potential airway obstruction. Veterinarians report that as few as three or four caterpillars can kill a medium-sized dog. A single caterpillar can be lethal to a cat.

Warning signs to watch for after any walk in a pine area:

• Excessive pawing at the face or mouth
• Drooling or foaming
• Swollen lips, gums, or tongue (may appear darkened or bluish)
• Vomiting
• Distress or lethargy

If you suspect your dog has made contact: Do not rub the area — this embeds hairs deeper into tissue. Rinse the mouth gently with lukewarm water, then go directly to your vet. Do not wait to see whether symptoms develop. This is a genuine emergency.

For full identification photos, the complete symptoms list, and treatment information, see our processionary caterpillar guide for Spain.

How Dangerous Are Processionary Caterpillars to Humans?

Adults are generally less vulnerable than dogs, but children are at meaningful risk. The caterpillar hairs cause urticaria (hives), intense itching, and redness on any skin that makes contact. Eye exposure causes conjunctivitis and can cause temporary vision problems. People with asthma or allergies may experience respiratory symptoms if hairs become airborne — which can happen when caterpillars are disturbed or on windy days near active processions.

How Can You Protect Your Family and Pets This March?

On walks:

• Keep dogs on a short lead in any area with pine trees throughout February, March, and April
• Scan the path ahead for processions — look for a line of caterpillars moving in single file, typically 5–30cm long overall
• Do not let children crouch over or touch caterpillars even with a stick — hairs can become airborne
• Avoid pine forested paths during and immediately after windy days (hairs travel)

At your property:

• If you have pine trees, check trunks and lower branches for silk nests (white or grey, oval, roughly the size of a rugby ball)
• Install physical trunk barriers — bands of grease-coated material around the trunk — to intercept descending caterpillars before they reach the ground
• Contact your town hall or a licensed pest control professional to arrange nest removal; most offer this service in winter months

For dogs specifically:

• Consider an alternative to pine forest walks until late April
• Brief your dog-sitter or walker on the risk if they are not local
• Keep your vet’s emergency number stored in your phone

How Is Climate Change Affecting Processionary Caterpillar Season?

This earlier and more intense season is not an anomaly — it is a trend. Research published by Spain’s National Research Council (CSIC) has documented a consistent advance in the processionary caterpillar’s descending date of approximately six days per decade since the 1980s, driven by rising winter temperatures. The species is also expanding its range northward and to higher altitudes, reaching parts of the Pyrenees where it was historically absent.

For property owners and expats, this means the risk window is extending. What was historically a 6-week period of heightened danger is now closer to 10–12 weeks in warmer coastal areas. Treating it as a year-round consideration rather than a brief seasonal hazard is increasingly the right approach.

Reporting and Local Resources

Most Spanish municipalities have dedicated environmental or pest control departments that handle processionary caterpillar reports. The usual process is straightforward: report the location via your town hall (ayuntamiento) website or phone, and the technical team will assess and respond — usually within a few working days for urban green spaces.

In rural or periurban areas managed by regional governments (comunidades autónomas), contact the relevant environment department. In Andalucía, this is the Consejería de Sostenibilidad; in the Balearics, the Departament d’Agricultura i Medi Ambient.

If you are a property owner in a comunidad (residential community), check with your administrator whether the community has a contract for nest removal in shared green areas — this is increasingly standard in urbanisations with pine trees.

For help finding a licensed pest control professional near you, see our guide to pest control companies in Spain.