Spain’s Guardia Civil has issued a social media alert about a pressing danger to children and pets during walks in parks and woodland. Despite their harmless and almost strokable appearance, processionary pine caterpillars represent a significant risk to the health of children and animals, especially dogs. 

These caterpillars have string-like hairs that can cause severe reactions in animals on contact with the skin or mucous membranes, releasing a toxin. This causes irritation, inflammation, and, in severe cases, necrosis – the death of body tissue. The Guardia Civil recommends that residents and tourists take extreme precautions when walking their dogs or with children and avoid areas where the presence of caterpillars has been detected. If you suspect that your pet or child has come into contact with them, it is crucial to act quickly to prevent them from digesting the toxin – thaumetopoein – which could worsen the reaction. 

During the winter, processionary pine caterpillars take refuge in silk bags on pine trees. As the larvae mature, they descend in the characteristic procession from which they have taken their name. They then look for a place to bury themselves to pupate and become a butterflies. 

It is at this moment they release their stinging hairs as a defence mechanism. When stressed or threatened, fifth-stage larvae actually eject hairs shaped like harpoons, which penetrate all areas of exposed skin nearby and irritate them. 

Global warming is forcing the species, which is considered an economic pest, to affect forests progressively further north. It has been a common pest in Southern European forests since classical times, but it has already reached the north of France, according to a 2010 study. 

The most common symptoms of contact for children include rashes, intense itching, inflammation and, sometimes, severe allergic reactions. Parents should therefore remain vigilant and prevent children from approaching or touching these caterpillars. 

The stinging hairs are also deadly to dogs. The most common symptoms include lesions on the tongue, excessive drooling, swelling of the mouth and throat, and difficulty breathing. In severe cases, it can cause anaphylactic shock and require urgent veterinary attention.

It is recommended to keep your dog on a lead when walking near pine trees or wooded areas where the insects might be.

Last week, the Costa del Sol region of southern Spain saw a surge in the number of processionary pine caterpillars, especially in Malaga. The National Association of Environmental Health Companies (ANECPLA) has called for much more to be done in council prevention plans in the spring and autumn seasons to minimise the harmful effects of these insects.