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Processionary caterpillar

The pine processionary caterpillar is the best known of all the processionaries, the insect is found in the warmer regions of southern Europe, the Near East, and North Africa.  It is the habit of the caterpillars to move over the ground in long head-to-tail processions and to sting with urticaring hairs, anyone who attempts to molest them that has brought the caterpillars to the attention of the public.

  It is also one of the most destructive of forest insects, capable of defoliating vast tracts of pines during its episodic population surges. The insect is active only during the colder times of the year, spending the warm summer months as a pupa buried in the ground.  The moths begin to emerge from the soil in August and shortly thereafter mate and seek out pine trees where they place their eggs.  Each female produces a single egg mass which it fastens to a needle of a suitable host trees.  Egg masses contain up to 300 or so eggs and the caterpillars typically enclose from them four or more weeks after they are laid.  The eggs are completely covered with scales that detach from the abdomen of the female.

Despite their small size, the newly hatched caterpillars have remarkably strong mandibles and are able to penetrate the tough needles of the host from the start. 

The caterpillars are highly social.  At first they are nomadic, spinning and abandoning a series of flimsy shelters constructed by enveloping a few needles in silk but in the third instar they initiate the construction of a permanent nest and settle down to become central place foragers.  There are no definitive openings in the shelter that allow the caterpillars to enter and exit. Rather, the caterpillars force their way through the layers of the shelter as they move in and out. The frass that is produced as the caterpillars process their meals accumulates at the bottom of the shelter.  

The caterpillars feed overnight then return to the nest at dawn.  The caterpillars rest in the nest during the day and at the elevated body temperatures they experience due to heating of the nest by the sun are able to efficiently digest the food they collect overnight. By March the caterpillars are in the fifth stage and are fully grown.  At this time they leave their nest, following each other in long, head to tail processions and seek out pupation sites in the soil.

While the caterpillars may form single file processions as the advance over the branches of the host tree in search of food, the most spectacular processions are formed when the caterpillars are fully grown and abandon the host tree in search of pupation sites.  Over-the-ground processions of as many as three hundred caterpillars have been observed.  The caterpillars may travel long distances from the natal tree looking for soft soil in which they bury themselves and form their cocoons  

The caterpillars of the pine processionary are highly urticating in the third and subsequent  stages.  Contact with the hairs causes skin rashes and eye irritations. Susceptible individuals may also develop an allergic response to a protein associated with the hairs of the caterpillar. 

Why are we writing about this caterpillar? Our dogs – and cats are inquisitive! They will be attracted by the movement and the glittering in the sun. Upon contact with the nose, lips or tongue the hair of the caterpillars will cause an immediate burning reaction followed by an allergic reaction that can vary from a 3x swollen tongue to death by shock. The first thing to do is flush the mouth out with loads of water! Then seek veterinary assistance. If you live far away, please contact us; we can instruct you!

Wherever you are in February of March, check the pine trees for the white fluffy nests. Avoid taking your dog there! If you cannot avoid them, then keep your dog on a short lead. If you live around these nests, then get them taken away (do not try it yourself! Because they cause severe eye and skin irritation), and have the pine trees treated in August.

Nazli Kreft van den Kieboom

Pointer Veterinary Clinic – Estepona.