Why You Need to Know about Processionary Caterpillars

It’s Spring, at last (at least it was a few days ago – it’s raining again today and feeling more like Autumn again, but hey ho.) At this time of year everything comes alive and the ground starts crawling with critters. Most of these are harmless, friendly even, but then there are a few others we have to watch out for. One of the most prolific of these is the pine processionary caterpillar which, after having spent months in their fluffy-looking nests high up in the pine trees, make their way down to earth for the final stage of their life cycle (as caterpillars) where they then burrow into the ground in order to pupate, hatching a short time later as the Pine Processionary Moth (Thaumetopoea Pityocampa).

A silk cocoon hanging on the tips of a pine tree

Silk Cocoon of the Pine Processionary Caterpillar

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The Distinctive Pine Processionary Caterpillar

I first saw these on a walk with DS and DD last year. At the time we didn’t know what they were but luckily I knew better than to touch an unidentified furry crawly and rightly too, as it turns out. Because as harmless as they appear – how much damage can a small fluffy looking caterpillar do? – they are in fact quite toxic. Not so bad to healthy humans;  we can expect a rash, which can be pretty nasty – the picture on Google images don’t look all that appealing but, risk of anaphylactic shock aside, it’s usually a localised reaction somewhere on the body and eventually clears up.  As with all things of this nature it’s best to keep your kids from picking them up or rolling around on the ground anywhere where they’re likely to be found. For dogs (and sometimes cats – although cats apparently keep their distance more often than not) they can be fatal, as a friend living in Spain, so a few weeks ahead in the life-cycle, discovered just a few weeks earlier. Her dogs made it, luckily, but it was a close shave and one she could have avoided if she’d known more about the dangers beforehand.

Personally, while I’m usually quite nervous of pests (and general pestilence) in this instance I’m mostly just relieved they’re not spiders – which is what I thought they were when I first saw the giant cocoons on the tips of the tree branches. But then I don’t have dogs. For any doggy owners, there’s some really useful information on this website and a very thorough write up of a doggy encounter with them on this other blog, ouiinfrance.com. In short, to protect your animals you need to prevent them from having any contact, not only with the caterpillars themselves but also with the spines, which are the cause of the problems. If they have an encounter with any caterpillars the advice is to get them to the emergency vet, so if this is you – go now. Go!!

The question I have though is how to get rid of them and what is being done about it because they really are prolific and I can see that if no action is taken this problem is only going to get worse. In future we may end up in closer proximity to them – while they’re around now there aren’t any particularly close by so unless my cats wander off into the woods, which are about 1/4 of a mile up the road, they’re unlikely to come into direct contact with them.

While these are common across much of Western Europe, different countries have different policies, as you’d expect. In France there’s a directive which places the onus on the land owner but requires action at the local level to be enforced. All good with the obvious problem that unless it’s enforced – and I’d say from the number of nests around here that it isn’t –  it’s unlikely to make the least bit of difference. Plus there’s so much land and so many owners, many of whom are scattered over the entirety of the globe, which means and not all land has an obvious owner, or at least not an owner on hand to actively manage it. Since the pesticides that were used to eradicate them are now banned (good) the best methods involve removing the nests and burning them (not good since fires can easily get out of hand and the act of removing the branches/nest can spread the dangerous hairs) or traps, which are the most ecological solution. The basic principle of the trap exploits a weakness in the caterpillars programming. You see these creatures, once they leave the nest, head to tail, seem to have no compulsion to go around anything, so as soon as they hit the barrier they just go round and round. Or rather, the first one goes round and round and the rest just follow! This discovery was thanks to a French naturalist, Jean Henri Fabre, who wrote a book entitled The Life of the Caterpillar (which is available to read online) about them. One day while studying them he managed to coerce them into forming a loop, so they were all equally following and leading, walking in circle. To his surprise them they continued this way for the best part of four days. Fast forward to today and four days is ample time for a trap to be set up and emptied. Game on.

The traps are designed so that a small tube leads out of the barrier into a collection bag, which you can then dispose of safely. There’s an official product, called Eco Piège, which you can pay upwards of 35 euros for (yeah, right), or you can go DIY.  Some cheap and cheerful DIY barrier ideas include using pipe lagging, some pipe and a bin bag, as in the picture below, posted by Linda Garnett to Facebook.

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DIY Processionary Caterpillar Trap using Pipe Lagging

Another simple idea used recycled water bottles – but of course now I can’t find the photograph to share. Also I’ve seen pictures of clear plastic gaffer-taped to the trunk of the tree, kind of like a large buster collar (the kind you put on your dog or cat to stop them scratching their stitches out). However you do it, the best approach seems to be one that involves funneling them into a container that you can easily seal in order to limit your contact with them.

As an alternative to catching the live caterpillars and then having to dispose of them, Farber recommends checking the tips of the trees for eggs and removing the branch tips before they hatch, so no cocoons or dangerous fibres to have to deal with. That might be a worthwhile approach if you’ve only got a few trees in a fairly small area and can easily keep a close eye on them but on the scale of the problem as it seems to be around here, that would be a lot of work!

So there you have it. You have been warned! Personally I hope I never have to put up with these on my doorstep but, if I do, at least I’ll have some ideas about how to get rid of them. And in the meantime I’ll be keeping myself, my pets and my kids well out of their way!

28/04/18 Update – I managed to get an up-close cocoon shot so have added it above. 

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4 Comments

    1. I’ve just added a pic of a nest/cocoon. Are they the ones you saw? At this time of year they’re quite heavy and a bit grubby looking but they start off like small balls of white fluff, like candifloss, on the tips of the tree branches.

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  1. I saw lots of white silk nests in pine trees, especially near the Col de Saint-Louis between Laval and Caudies-de-Fenouilledes. I assumed they spider nests but now I think they are more likely processionary caterpillar nests. Do you happen to know?

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