Tree Pests: Pine Processionary Caterpillars

Cocoon of pine processionary caterpillars

I trained my binoculars on the tree and zoomed in. My suspicions were confirmed. There was no doubt that the beginnings of a white cocoon about halfway up were the work of pine processionary caterpillars. If you look closely, you can even see one hanging off the bottom of it. Their tell-tale cocoons can be seen in large numbers in some pinewoods, and they are among the most devastating of tree pests in Europe.

The caterpillars are the larvae of the Pine Processionary Moth (Thaumetopoea pityocampa) or chenilles processionaires du pin in French. They live together in colonies in the tent-like cocoons that they spin in pine trees. The caterpillars make nightly sorties to feed on the pine needles. They can wreak terrible damage on the trees and are a considerable problem in parts of central and southern Europe.

When they come out at night to feed, the caterpillars lay a pheromone trail on the tree. This enables them to assemble at feeding sites and to find the nest again after feeding.

Pine processionary caterpillars on the move

When the caterpillars are ready to pupate, they march in file down to the ground where they disperse and pupate singly just beneath the surface. The photo shows a chain of caterpillars, seen on one of our walking group’s outings in March a few years ago. I had never seen this before. The moths emerge in late spring.

Our pine tree

I am very attached to our pine tree. When we first moved here nearly 20 years ago, it was the same height as us. Since then, it has grown hugely, both upwards and outwards, and is quite a feature in our garden. I am outraged that they’ve managed to get to our tree, since there are no others close by. I imagine, though, that the moths can travel long distances.

In fact, we had a cocoon in it some years previously, but it was closer to the ground and more easily dealt with. That seemed to sort them out on that occasion. To get at this one, we’ll have to climb up the tree (a ladder can’t get in there), clad in protective clothing, remove the branch and burn it.

If you plan to deal with similar cocoons, be warned. The caterpillars should never be touched, nor the cocoons, since the hairs on their bodies cause extreme irritation to the skin. Keep children and household pets well away from them.

In addition to removing carefully the branches concerned and burning them, these pests have a number of natural predators. Some birds eat the caterpillars, while hoopoes eat the pupae and bats eat the adults. A parasitic wasp also kills the larvae. Since the hoopoes will be arriving here soon, I hope they make a bee-line, as it were, for our tree.

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    • These caterpillars are not to be taken lightly. They can cause significant skin irritation, so it’s a good thing to be able to identify them in advance.


  1. The pine forests here are full of them, I loathe them. Recently we have seen long long lines of them across the tennis courts which are surrounded by pine trees. Have a lovely weekend xx

    Liked by 1 person

  2. Years ago we spotted these cocoons in the pine trees in the jura but it was only in the last couple of years we discovered their awful secret. La depeche regularly carries warnings about keeping dogs away from them when out walking. I hope natural predators deal with yours before you have to go in for some ‘grimpeur’ work! And fingers still crossed for the latest submission. 🙂

    Liked by 1 person

    • I think we will have to do the grimpeur work anyway. We can’t rely on natural predators to do it…Thank you for your crossed fingers – I will let you know when/if you can uncross them!


  3. Amazing! I had no idea what these caterpillars were when we stumbled on several columns of them in Cantal a fortnight ago. I took pictures of them intending to research but hadn’t got round to it and now, courtesy of you, I know all. In fact the South of Cantal has a fair amount of what is known as Gypsy Moth in the US … my husband identified it for me a few years ago but we had not connected the caterpillars. I do know Gypsy Moth is a dreadful nuisance in New England and hope you can deal with your pests. Though the processing caterpillars are rather a wonderful sight.

    Liked by 1 person

    • Whatever you do, don’t touch them – and don’t let the Bean near them! Every tree seems to have its pests. After Dutch Elm Disease, there’s something attacking ash trees and another one having a go at oaks. What with these caterpillars going for pine trees, it could be a disaster. I think if we deal with it quickly we might stop them, as before. But they will come back another year, no doubt.


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