The pine processionary caterpillar, a serious threat to dogs and cats in Spain

The hairs of the caterpillar can kill inquisitive pets when the insects drop to the ground from their nests in pine trees

The pine processionary (Thaumetopoea pityocampa) is so called because members of the species in the caterpillar phase of their life cycle, before they metamorphose into moths, form nose-to-tail processions as they leave their soft cocoon nest of spun filaments, The species is widespread throughout the warmer Mediterranean areas of Spain and other parts of Europe.

The favoured nesting grounds of processionary caterpillars are higher up in pine trees, where the nests are closest to the winter sun, and it is normally in late winter and early spring that the caterpillars drop from the cocoon nests and form "processions" in search of soft, warm earth in which to pupate. There can be hundreds of caterpillars nose to tail, winding along roadways or rough ground, and although they may appear innocuous they can be lethal to animals and cause serious reactions in humans, especially young children.

The caterpillars have poisonous and irritant brittle hairs on their bodies, which can easily be ejected should the caterpillar feel threatened. These hairs penetrate the skin easily and cause instant irritation with an urticating protein (i.e. one which stings or irritates). The caterpillars are a mottled dull brown with faded yellowish splotches, but are instantly identifiable as they travel in chains along the ground.

Dogs and cats are often attracted by the bittersweet smell and taste of the processionaries, and both may try to eat them. The results can be fatal; as few as three or four will kill a medium-sized dog, and just one may produce death in a cat as the hairs become embedded in the tongue of the animal, and generally causes necrosis of the tongue. By the time the owner notices the problem, it is usually too late for veterinary treatment to do much except ease suffering.

Initial symptoms to watch out for in a pet include vomiting and tongue swelling, although it is often immediately apparent that there is a problem as the animal will attempt to rub off the hairs of the caterpillar, which only irritates the inflammation further.

It is highly advisable not to walk dogs in areas where there are large numbers of processionaries, as loose hairs on the floor can be just as lethal for an animal, and it is certainly vital to keep pets on the lead in forests where there are processionaries on the march.

Disposal of processionary caterpillars

These animals are most vulnerable whilst still in their silvery nests high up in the pine trees, so this is the best time to dispose of them. Wearing eye protection, gloves, and covering as much skin as possible, cut the nest carefully out of the tree with long handled pruners, attempting to keep the nest intact, put it in a plastic bag and throw it in a bin.

If the nests are low down, spraying with hair spray first will stop the hairs flying off and spraying with insect spray or fly spray before putting in a plastic bag helps to eliminate them completely.

Do NOT touch with bare hands; use disposable gloves, preferably thick rubber or plastic, and definitely do not use cotton gloves as the hairs can stick to these and continue to irritate.

Knocking the nests out of the tree is very dangerous, as the hairs can fly around in the air and settle on the ground, where they can be picked up by animals and also cause irritation for humans, particularly those who fail to wear goggles.

Burning is not advisable unless you have a hot fire going which can incinerate the branches immediately. Lighting a bonfire containing the nests still gives the opportunity for hairs to fly into the air.

Once the caterpillars are on the ground they are very dangerous, as everywhere they go they leave trails which are enough to kill a dog or cat.

The importance of taking these unusual caterpillars seriously cannot be overstressed: every year readers of Murcia Today report losing pet dogs as a result of them having taken insufficient precautions, or a simple excess of curiosity on the part of the dog. Those who have lived in Mediterranean coastal areas of Spain for a number of years have learnt over time to keep an eye out for the caterpillars from the New Year onwards, and accept their inevitable appearance as just another aspect of the changing of the seasons, 

At the same time, if you have a pine tree providing shade in your garden, keep an eye out for the cocoons: by cutting them down and disposing of them before the caterpillars emerge you will not only be doing yourself a favour, you will be helping out the whole of the community in which you live.