Beware of Processional Caterpillars

Ever noticed that some pine trees have sacks made of what looks like spiderweb up high in the tree? These are the communal nests of the notorious Pine Processionary moth caterpillar. If you have pine trees on your land you would be wise to buy the trunk bands with a plastic bag full of soil attached that act as a trap for the caterpillars as they descend. Garden centres sell them.

The caterpillars are a danger to you, and more especially to your pets. The caterpillar hairs are urticating, which means that they cause an allergic reaction if they touch flesh. You will most likely just get itchy red spots on your arms, but your pet may ingest the hairs by sniffing the caterpillars or licking their own fur where the caterpillar hair may have settled. This can lead to tragic consequences.

The caterpillars live in the web nests from autumn to spring. Every evening unless very cold the caterpillars emerge in single file to feed on pine needles. They are a serious pest of pine forests. One day in spring they form a single file procession behind one of the female caterpillars. They descend from the tree and the female leads them to a patch of ground where they will bury themselves in the earth to pupate. Forestry managers have discovered that they can be tricked into thinking groves of deciduous trees planted amongst the conifers are open ground suitable for pupation. The trees come into leaf after the caterpillars pupate, leaving them in the shade and many of them die. The caterpillars have extremely irritating hairs which hang in the air and fall from the nests long after the caterpillars have vacated. Neither the nests nor the caterpillars should be handled, and pet owners need to be on their guard in case animals are exposed to irritant hairs. The rash generally lasts about 3 weeks and should be treated initially by taking a hot shower as soon as possible after exposure, and washing clothes exposed in hot water. Pets which are exposed should be seen by the vet as soon as possible, as in severe cases, exposure can lead to necrosis of the tongue, requiring amputation or even causing death. 

Scientific Name: Thaumetopoea pityocampa.

English Name: Pine Processionary Moth.

French Name: les Processionnaires du pin (='pine processionaries').

Lookalikes: Oak Processionary Moth T. processionea, however these are only associated with oak woods, not pine and the moths have discoloured hind wings. I've only ever seen these once in the area, in the Forest of la Guerche. Don't confuse with other very hairy caterpillars such as the Tiger and Eggar moths. If you see a hairy caterpillar all on its own, it is not a Processional, so don't squish it, even just in case.

Habitat: Pine trees and the ground nearby. All types of conifers with Black Austrian Pine being the preferred host. The caterpillars seem to choose open ground to bury themselves for pupation. Depending on the weather, the caterpillars could start appearing in long lines on the ground as early as February, but usually it is March or April here in the Touraine. 

 

Red spots caused by Pine Processional caterpillar hairs. In this case the person picked up a cat which had been outdoors and had the urticating hairs on its fur.

NOT a Pine Processionary caterpillar. This is a tiger moth caterpillar -- darker and all on its own.

NOT Pine Processionary caterpillars. These are Glanville Fritillary butterfly caterpillars - rare and precious. They are black with red heads, not ginger and grey, much smaller than processionary caterpillars, and their web nest is on the ground, usually over a plantain plant.