Not a sight you want to see on a pine tree

This is the nest of the processionary caterpillar. Walk up to La Pedrera and you will see literally hundreds of them on the pine trees. Eradicating them on the thousands of pine trees up there would be an impossible task. The little yellow plane may spray the area to control them but still they will persist.

It is at this time of the year that you will find the processionary caterpillars coming out of their nests and forming conspicuous snakelike lines as they traverse the ground searching for soft soil to burrow into.

They might look fascinating to watch but the best advice is to avoid these innocent looking creatures at all costs. The caterpillars are covered in tiny barbed hairs which are their defence mechanism. These hairs are often being shed and so can be airborne around infested pine trees, on the branches where they have travelled and also left in the line of the migrating procession.

When humans and our pets come into contact with these hairs, they can cause reactions ranging from mild inflammation and irritation to severe anaphylactic shock. The worst problems occur if you make contact with the caterpillar directly and ingest the hairs, either by picking it up, stepping on it or moving them in some manner. Once on your skin a rash soon forms which can be incredibly itchy. Medical advice should be sought if you are unfortunate enough to experience this. The rash can be painful, very itchy and lasts for as much as three weeks.

Moving the caterpillars, their nests, or even the branches that they have walked along, may release these hairs into the air where they can be inhaled or come to rest unnoticed on clothing. The nest material that remains on the tree after the caterpillars have left will still contain the “urticating” hairs. Even burning infected pine branches should be avoided as the hairs can be lifted into the air and fall anywhere or be inhaled.

Inquisitive dogs can get too close to the intriguing procession of caterpillars and may pick up the hairs onto their paws, these irritate and so they lick them. Once the hairs are on the lips/tongue it will induce itching, swelling and possibly vomiting. The symptoms are small white spots in the mouth and on the tongue, excessive drooling and chomping. In some cases partial amputation of the tongue is the only course of action.

Under no circumstances should you try to handle the caterpillars, cut down the nests or try to burn them.