People who are native Portuguese or ‘estrangeiros’ who live here will be aware of these little beasties, but it doesn’t hurt (probably not the best term to use under the circumstances) for a refresher, and a warning to newcomers, who might not be aware of them. If you live in an area with pine or cedar trees, you really need to read on.

Every year from late winter is the time to be on the lookout for what looks like a furry snake, but it is in fact a line of caterpillars, nose to tail, you would be wise to avoid. Already you will be able to see their silky nests built by the larvae, high up in pine trees, and these were laid as eggs by the completely harmless processionary moth Thaumetopoea pityocampa.

The adult is an innocent looking stout furry moth that holds its wings like a tent over its body. Each female moth lays an enormous number of scale-covered eggs near the tops of pine trees, the eggs actually mimicking pine shoots. After hatching, the larvae munch away on pine needles while progressing through their five stages of development. To survive through the winter, the caterpillars construct a nest of silk threads that are visible high in the pine trees, making them one of the few species of temperate zone insects where the larvae develop in winter. Any time in the spring from February onwards, when they are ready to pupate, the caterpillars leave the nests in a long line - a ‘procession’ - for which the species is known. They then burrow underground, pupate, and emerge between mid May and August.

The larvae are a major pest to coniferous forests, and are the biggest cause of pine forest destruction, being able to completely defoliate trees if large amounts of them are present. They live communally in these large silky looking nests, and there are often several such nests in a single tree.

But it is the ‘hair’ which is dangerous. They defend themselves from predators with conspicuous hairs containing an irritant chemical, and simple contact with these hairs can cause severe rashes and eye irritation in humans and animals, with some people possibly suffering an allergic reaction. When stressed or threatened, fifth-stage larvae will also eject hairs shaped like harpoons, which penetrate all areas of exposed skin nearby and irritate them. An unwary dog, for instance, can get inflammation of the mouth, tongue, and lips when it licks or gets a caterpillar in its mouth. In the most serious cases, they might even lose part of the tongue and lips.

And it gets worse - If your pet swallows one, it might cause inflammation of the larynx, which might compromise breathing, and possibly lead to the death of the animal. If the hairs are carried from the nests by the wind, they can cause inflammation of the eyelids, ulcers in the cornea of both animals and humans, and cause inflammation of the nasal cavity if the caterpillar or its nest are sniffed.

processionary caterpillars

All in all, the pine or cedar trees should be checked out before getting close! If you suspect that your pet has been in contact with these hairy little devils, the best advice is to take them immediately to your vet, who will evaluate the seriousness of the injuries, and prescribe the most suitable treatment.

It is recommended that if the tree is on your own land, you spray the pine trees with biological insecticide during the months of October and November, as it is during this period that the caterpillars are newly hatched. If you can safely reach the nest, and it is small enough, try to remove it. Wear gloves and clothing which covers as much of your body as possible, and detach the nest from the tree. Remember to change your clothes afterwards to ensure no part of the nest is attached to you. As soon as the nest is on the ground, and if you can do so safely, burn it to make certain its occupants are dead. In extreme cases, you might even want to go as far as removing the tree completely.