A dangerous procession in my path

With the trail passing by woodland, I saw an interesting behavioural manifestation of a group of small but quite deadly creatures. Adult pine processionary caterpillars leave their nests up in the pine trees and crawl in large groups, forming a single line. They actually travel for lengthy distances, until finding soft ground to burying themselves, forming cocoons and, later, emerging as moths.

It is also in this later adult stage that they can become deadly as their only defence against predators is their hairy spikes. These, upon contact, can cause severe rashes and even allergic reactions. Moreover, when under stress, these caterpillars eject their hairs which cling to the predator’s skin, eyes and respiratory airways. Dogs, with their curiosity, easily fall severely ill and may perish from just sniffing these caterpillars. Fortunately, this deadly procession only lasts a couple days a year, commonly occurring in the first warm days of spring.

These caterpillars are a devastating plague for pine woodlands. However, they have become a plague because of former agricultural policies which replaced autochthones forests with monocultures of their preferred habitat: the pine tree. Moreover, the natural predators of these caterpillars, crickets, bats and several birds’ species, fail on having natural environments to successfully breed in sufficient numbers to control the population. One major issue of forest farming is that trees are taken down without aging enough to provide natural shelters, i.e. small cavities, for birds to nest. One possible contribution would be to provide, in the affected regions, artificial nests for predators such as the great tit.

Pine processionary / Lagarta processionária do pinheiro - Thaumetopoea pityocampa Schiff. 

Serra do Gerês, Portugal
2017, March