The Processionary Caterpillar - Danger

These hairy, up to 5 cm (1.8 inches) long caterpillars are the larvae of the gray processionary moths (Thaumetopoeidae) belonging to the superfamily of prominents (Notodontidae). There are several species of these moths. In Southern Europe, the Pine Processionary Moth is quite common whereas the Oak Processionary Moth is becoming quite widespread in Germany. The adult moth itself presents no danger.

In spring, you can see white tent-like nests in the pines, similar to cotton wool, in which the larvae of the Pine Processionary Moth develop. The nests of the Oak Processionary Moth are less obvious and are usually found as weaves on the trunk and the branches of the oaks.

Pine Processionary Caterpillars

Oak Processionary Caterpillars

When the weather is getting warmer, the larvae are leaving their nests during the night looking for food. They can, however, also be observed during the day. They move in long nose-to-tail files, hence their name processionary caterpillars. Towards the end of spring, the larvae march in their usual fashion to the ground, where they disperse to pupate singly on or just below the surface.

Processionary caterpillars

The very fine urticating hairs of the larvae contain a cocktail of nettle toxins, primarily Thaumetopoein, and even light contact causes extreme irritation to the skin and other allergic reactions in humans such as asthma, etc.

The tiny hairs easily loosen from the larva's body and in case of danger the larvae can actively launch the hairs off against the enemy. The hairs are easily spread by the wind and can thus be a danger to the dog not only in spring as the toxin remains active for a long time.

These fluffy-looking larvae arouse the dog's curiosity and he may playfully hit them with his paw. When wounded, the larvae secrete an acidic poison which stings painfully upon contact with the skin. To ease the pain, the dog starts to lick his paw thus effectively spreading the poison to his mouth where it can cause severe tissue damage.

Dogs are greatly exposed when walking about with their nose to the ground as the mucous membranes of mouth and nose are particularly sensitive. If a dog touches such a caterpillar with his muzzle, his tongue can swell up within no time and it can lead to heavy poisoning and burns on the muzzle and in the mouth.

Here are a few examples:
In Spain, a West Highland White Terrier was suddenly listless and stopped drinking and eating! He started trembling and his tongue started to swell. Despite immediate veterinary attention, the dog fought for his life for one week and lost part of his tongue.
Also, a Labrador barely survived and lost part of his tongue.
In the region of Lausanne, the French speaking part of Switzerland, a French Bulldog had to have part of her tongue and lip removed as the tissue had become necrotic from the burns. She too spent 7 days at the Veterinary Clinic in Berne.

The hairs can also cause serious damage when they get embedded in the eyes.

A close encounter with these larvae can thus be a life-threatening experience for the dog. In case he starts rubbing his nose and muzzle on the ground, has froth around his mouth and his tongue or head starts swelling up, it is highly probable that he was in touch with these larvae. As a first aid you can pour water over the affected parts, but be careful not to touch affected parts with your bare hands.

Processionary caterpillar poisoning is an absolute emergency and a vet will have to be consulted without delay.

If you find yourselves in an area where you see these conspicuous nests in the trees, keep your dog on the lead, or better still, avoid the area.