| Processionary Caterpillar |
| Wild Mallorca |
The pine processionary caterpillar is one of the most well known of all the processionaries and were studied as long ago as 1736 by Raumier and later in 1898 by Fabre. Fabre wrote an essay "The life of a caterpillar" which is among the classics of popular entomological literature. This caterpillar is found in warm regions such as southern Europe, the Near East and North Africa. It is prolific in Mallorca and you are warned to stay well away from them! Apart from being one of the most dangerous forms of caterpillar it is also one of the most destructive of forest creatures. They are capable of defoliating huge tracts of pine trees during their episodic population surges. Strangely enough they have also been recorded as being one of the most social of caterpillars - among themselves naturally. Siblings are known to stay together throughout their larvae stage and often pupate side by side buried in the soft soil found when they formed their long, above ground, head to tail processions. These creatures are only active during the colder times of year and spend the very warm summer months buried in the ground in their pupae form. In August they begin to emerge from the soil and mate shortly after this. Once again they seek out pine trees to place their eggs so that their 'offspring' have the perfect place to feed when they hatch. The females produce an egg 'mass', which contains up to 300 or so eggs,and fastens it to a needle of the pine tree. The eggs are covered with scales that come away from the female's abdomen as they are produced. Even though the newly hatched caterpillars are tiny they have incredibly strong mandibles and are able to penetrate the tough needles, of the host pine tree, immediately upon hatching.  As said before these are social creatures. The appear to go through a learning process as they spin and abandon at least two flimsy shelters before constructing their permanent nest from where they can feed and survive. This happens in their third instar. There does not appear to be any sort of entrance or exit in these shelters and it seems that the caterpillars force themselves through the layers of the shelter when moving in and out of it. As witnessed by anyone who has seen a nest hanging from a pine tree, the rubbish they produce as they process their food intake accumulates at the bottom of this shelter. Colonies of these processionary caterpillars are active throughout the winter months. Research shows that they leave their nests soon after sunset and will forage from any part of the host tree no matter how far away the branches are. Once they have found their spot they will stay and feed overnight returning back to the next at dawn. For those of us who hoped that the frost would kill these creatures off, it has been observed that these caterpillars can forage on the coldest of nights and can move, perhaps not so fast, at sub-zero temperatures. They build their nests so that they are able to absorb solar radiation and during the sunny days when it is warm and well above ambient temperatures, this enables them to uses the elevated body temperatures experienced by the heating of the nest, to digest efficiently all that they had consumed overnight.
Around March the caterpillars have reached the firth instar and are fully grown. This is the time that they leave their nests, and following each other in long, head to tail processions, begin their journey to seek out pupation sites in the soil.
 Recent studies have observed that the caterpillars excrete a trail pheromone as they move over the branches of the host tree. This unidentified marker is produced when the tips of their abdomens brush against the substrate and pine processionary caterpillars are able to distinguish between old or new trails or even the amount of caterpillars making the trail. They then follow the trails marked by the most caterpillars. Making trails allows the caterpillars to gather at feeding sites as well as guiding them back to the nest once they have finished feeding. These caterpillars move over the branches using these trails, either head to tail in groups, or independently. The caterpillars often move around the host pine tree in single file processions but because of where they are (up high in the pine tree) they are seldom observed, making the appearance suddenly of spectacular processions of these creatures moving over ground with up to as many as three hundred caterpillars in a row, quite disconcerting. These caterpillars are also quite prepared to travel long distances in order to find the soft soil they need, to bury themselves, and form their cocoons.
For those unfamiliar with these caterpillars please take heed. The best advice to give is to keep well away from them at all costs. We discovered these creatures, which I have to admit I did not know existed, when moving to live in Mallorca. Having dogs, which we walk regularly in the local forest, we were very lucky to be told about them before experiencing too much of a problem. Having said that we had to rush our Alsation/Husky to the vet in Palma one evening when he developed a problem with swallowing and breathing. It really is quite traumatic and we found out the next day that hairs from a nest in a tree just ten metres away from our terrace could very well have flown onto the terrace and he had - we are only surmising - perhaps tried to lick them from his paws which were itching. Amazing considering the lengths we had gone to avoid contact with these creatures during our dogs' daily walks.These caterpillars are covered with tiny barbed hears with can hardly been seen and are their defence mechanism. Unfortunately for us these hairs are often being shed and are airborne around any of the pine trees carrying their nests. They will also be on the branches and ground around the tree as well as on the trails they make as they migrate to their soft soil! Should any child, person or pet come into contact with these hairs it can, and normally does, have quite drastic consequences. The reactions vary from mild inflammation of the skin and irritation to a very severe anaphylactic shock. The most severe problems occur if you or your pets are in direct contact with the caterpillar and ingest the hairs either by picking them up, stepping on it, or moving them in some way. Medical advice should be sort immediately. Even when they have gone from the nest, the nest itself still remains a problem as it is full of these hairs, even burning the nests can cause problems as the fire will lift some of the hairs where they can fall on the ground or even be inhaled. Many vets have extra call outs, during the time that the caterpillars migrate, where inquisitive dogs have got too close to the procession, or may have picked up hairs on its paws and then licked them, causing swelling in the mouth and possible vomiting. The results of contact has been known to be fatal for small dogs and is dangerous for small children. Please avoid any locations with these caterpillars during the time when they are on the move with small dogs and children, should you suspect contact of any sort please seek medical attention immediately. |
