A moment's search turned up these web pages

dangerouswildlife

and more generally

thaumetopoea

From there I got the next information that might be helpful for you.

These caterpillars are called processional caterpillar because when hungry they will leave their cocoon and move from branch to branch to seek out food, traveling nose to tail in a line. These are found throughout the warmer regions of Southern Europe, the Near East and North Africa. In addition to causing widespread damage to pine trees, they are a major danger to small animals (including dogs) and, to a lesser degree to humans. Do not touch them as their very fine hairs are poisonous. The caterpillars live in silky cocoons in the pine trees, stripping them of their needles. They are most prevalent from January to mid April and are at their most dangerous in mid to late February. Evenings are when they can generally be seen walking in long lines going from tree to tree.

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 close 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.