The Procesional Pine Caterpillar

This is the most significant disease to affect Mediterranean Pines. The term “processionary” is used because the caterpillars travel together in long head- to- tail processions. Scientific name: Thaumetopoea pityocampa Schiff.

The processionary pine caterpillar does significant damage, especially to Pine Trees, although it can sometimes attack Cedars and Firs.
Pines: All species of Pine can find themselves affected, the favourites are The European Black Pine (Pinus nigra), The Canary Island Pine (Pinus canariensis), The Scots Pine (Pinus sylvestris) followed by the rest: The Maritime Pine (Pinus pinaster), The Aleppo Pine, (Pinus halepensis) and The Stone or Umbrella Pine (Pinus pinea).



Geographic distribution

The processionary pine caterpillar is typically Mediterranean and is found throughout Spain, Portugal, France, Italy, the coastal zones of Greece, Turkey, Syria, The Lebanon, Palestine, Israel, Egypt, Libya, Tunisia, Algiers and Morocco as well as in some regions of Germany, Switzerland, Hungry and Bulgaria.

In the summer the moths of the processionary pine caterpillar appear, they mate and the female lays her eggs on the leaves of the trees. The caterpillars hatch in 30-40 days, that is to say, between the middle of September and the middle of October. (Northern Hemisphere)

The caterpillars build nests or shelters, made of silk in which they take shelter during the cold of winter.

When spring comes or at the end of winter (from February to the beginning of April) the caterpillars descend to the ground in single file, from whence comes the ‘processionary’ name. They then pupate, burying themselves in the ground spun into chrysalides. The moths emerge from the chrysalides in summer, these will mate and a new cycle will begin.


Bundles of dry leaves produced when the caterpillars nibble at the leaves instead of eating them completely.

Visible silk nests or shelters appear in the tree with the onset of winter.

Caterpillars on the trunks, branches and on the ground.


The caterpillars feed in winter on the leaves of Pines and Cedars, causing the leaves to dry up and fall to the ground. The worst damage is done between the end of the winter and the middle of spring when the caterpillars are at their largest and hungriest. The defoliation rarely causes the death of Pine trees but it greatly weakens them and facilitates a later attack by other pests and diseases. Small pines may dry up. The aesthetic aspect of gardens is spoiled.

Care must be taken that children do not touch the caterpillars. The processionary pine caterpillar is dangerous to inquisitive domestic animals such as puppies if they touch or lick the ‘procession’ or a fallen nest or shelter, (cats are more cautious). The caterpillars have urticating hairs. If animals touch them they can produce the following symptoms: Inflammation of the lips, mouth and general area of the head. The animal tries to scratch itself and greatly slavers. A vet should be consulted.


There are various methods to control this infestation:

Biological insecticides
Growth inhibiting insecticides
Conventional chemical insecticides
The cutting and burning of the nests or shelters
Encouraging and protecting insectivore birds


Treatments may be carried out at anytime during the winter. It is best to do it when the caterpillars are young and more susceptible to the products and when they are lower down in the tree.

Mechanical elimination of the nests/shelter by cutting and burning is best carried out in warmer regions in the first fortnight of December and in cooler areas around the middle of November.

Between February and March the caterpillars are fully grown and this is when they descend to the ground.

The flying season begins in summer. As a guide, we can say that the earliest colonies, found in cooler areas start to fly in the middle of June and the later ones in September.


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