Pine Processionary Caterpillars and Dogs: a Silent but Potentially Deadly Danger

processionaria - dettaglio - photo by Katie Janest

What Are Pine Processionary Caterpillars?

The pine processionary caterpillar (Thaumetopoea pityocampa) is an insect that owes its name to its peculiar habit of moving in long lines, similar to a procession. It is the larval stage of a moth that primarily inhabits pine and cedar trees. Common in Southern Europe and parts of the Mediterranean, these caterpillars are most frequently spotted during late winter and early spring. Despite their harmless appearance, they pose a serious risk to both humans and animals, especially dogs.

Why Are They Dangerous for Dogs?

Pine processionary caterpillars are covered in tiny urticating hairs that contain a toxic protein called thaumetopoein. When a dog sniffs, licks, or accidentally ingests one of these caterpillars—or even comes into contact with a contaminated surface—the hairs can release this toxin, leading to serious allergic and inflammatory reactions. The danger lies not only in ingestion but also in simple physical contact. For dogs, who often explore the world with their nose and mouth, the risk is particularly high.

Immediate Symptoms to Watch For

The first symptoms of contact usually appear rapidly. These may include:

Excessive drooling and foaming at the mouth
Swelling of the tongue, lips, or muzzle
Difficulty closing the mouth or swallowing
Vomiting or sudden behavioral changes
Inflammation or necrosis of oral tissues

In severe cases, the necrosis can lead to the loss of parts of the tongue, and if the toxins are inhaled or ingested in large quantities, they can affect the respiratory tract or internal organs, making the situation life-threatening.

What to Do in Case of Contact or Ingestion

If you suspect that your dog has come into contact with a pine processionary caterpillar, do not delay seeking veterinary care. Immediate intervention is essential. In the meantime:

Avoid touching the affected area with bare hands, as the caterpillar’s hairs can also cause skin irritation in humans.
Rinse the dog’s mouth with abundant water, being careful not to rub the area to avoid further spreading the toxin.
Keep the dog calm and try to prevent it from licking or scratching the affected areas.

Your vet will likely administer anti-inflammatory and antihistamine medications, and in the most serious cases, begin treatments to counteract necrosis or systemic poisoning.

Prevention: The Most Effective Defense

The best protection against the pine processionary caterpillar is prevention. During the high-risk seasons—usually from January through May depending on the region—avoid walking your dog near pine woods or cedar trees where nests may be present. These nests appear as white, web-like clumps at the tips of branches. Also avoid areas where the caterpillars are known to descend in procession toward the ground.

Additional Tips

Always keep your dog on a leash during walks in wooded areas.
Observe the trees in your area and report nests to local authorities if necessary.
Consider informing other dog owners, especially if you frequent shared parks and trails.

Final Thoughts

The pine processionary caterpillar represents a silent but real threat to your dog’s health. Knowing how to recognize the danger and respond promptly can make the difference between a manageable situation and a tragic outcome. As always, prevention and awareness are the most effective tools we have to protect our four-legged companions.