The pine processionary (Thaumetopoea pityocampa) is a moth of the subfamily Thaumetopoeinae in the family Notodontidae, known for the irritating hairs of its caterpillars. THEY ARE VERY DANGEROUS!
The caterpillars have an extraordinary behaviour forming long head to tail processions, often many meters in length. They are found across Europe including Spain, France, Italy, Portugal, and Greece but with climate change they are being seen further north. They are also seen in Asia, the middle east and north Africa. The similar oak processionary moth was originally found in London but the range is expanding each year into the surrounding regions of Kent, Essex, Hertfordshire, Hampshire, and Berkshire.
There is a complex life cycle. In the late summer the adult moths lay their eggs high on pine trees. After hatching, the larvae start consuming pine needles while going through five moults or instars. During the first two instars the hairs are not developed and this is the time when natural predation by birds and other animals mostly happen.
By the winter the third instar has formed and they live in the white silken protective nests built to maintain ideal living conditions. At this point the urticating hairs are developed.
As the weather warms in early spring the caterpillars are ready to leave their nests and move down the tree in their characteristic procession. They move en mass for long distances seeking a suitable site. There they dig underground and pupate (sometimes for up to three years in this state).
At the end of the summer the moths emerge and start the process again however depending on weather and other conditions the pupas may stay in the ground for up to three years so this years moths might not be last years caterpillars.
The caterpillars overwinter in tent-like nests high in pine trees but in the spring fall onto the ground and march to new pastures: convenient sites where they can pupate. They have conspicuous hairs (known as setae) containing an irritant urticating protein, thaumetopoein, a small protein capable of provoking extreme inflammatory responses in animals (and humans) that come into contact with the hairs of the caterpillars. These hairs are shaped like harpoons, which penetrate all areas of exposed skin nearby and irritate them with the urticating protein.
As well as causing cutaneous and ocular inflammation (that can be very severe) they can also cause oral and pulmonary lesions if the hairs are swallowed or inhaled.
As well as having impact on humans and animals it can also have significant economic impact on coniferous forests of southern Europe, where the caterpillar is responsible for most of the defoliation seen in coniferous trees. Curiously outbreaks may be cyclical, with a period of 7 to 9 years. These delays are often seen with arthropod behaviour. Bizarrely prime number delays for pupation is linked to an evolutionary strategy observed in periodic arthropods, which emerge every 13 or 17 years (both prime numbers) to avoid predator life cycles. But this is another story!
Why have the poisonous setae evolved and why do the caterpillars express the poisonous barbs later in their life cycle at the time that the processionary behaviour manifests? It seems likely that the remarkable behaviour where the many caterpillars move as a single large unit makes the group seem like a much larger and intimidating entity to potential predators. Likewise the toxic hairs manifest themselves just at the time when the coordinated behaviour is seen, again maximizing their defensive attributes and hence survival. One can speculate that the coordinated evolution of the defensive hairs and a sophisticated group behaviour maximizes survival just when the caterpillars leave their initial nest seeking safe pupation sites,
Whatever the evolutionary background from a practical perspective the key thing is to stay well clear of these caterpillars.
Watch the amazing processionary behaviour from afar!
BUT DO NOT TOUCH!!
What to do if you touch one? Apply a piece of adhesive tape to the affected areas and pull the tape off immediately. This should remove the majority of the hairs and reduce the irritation. Wash all areas with copious amounts of water where itchy caterpillar hairs have been observed or where irritation occurs. Anti-histamines and steroids may help. Seek medical advice!
Craigavad golf 