Lethal danger: The pine processionary moth’s caterpillar


Living in France for over 10 years I was warned from the early days, when horse riding, to avoid the nests of the pine processionary moth (Thaumetopoea pityocampa or PPM). Recently I got a call of some friends, their dog was not well, breathing heavily, drooling and having a blue tongue after been in contact with these caterpillars. I immediately advised them to go to the vet, knowing the danger involved for their dog.

Many dog owners arriving in this region, have no idea of lurking diseases such as Leishmaniasis (caused by sandflies living in the area, breeding in moist soil containing organic matter, not in water!), which can be prevented with the Scalibor collar (more about this disease in my next post), let alone know the danger caused by the caterpillars, topic of this blog post.

Having several grandchildren and being a dog owner, I’m all for prevention. But it must be said, these creatures have been about for many thousands of years, are a food source for birds, their nests and caterpillars can easily be seen and they will only shed hairs for a reason… So let us not get panic attacks when not necessary, you can’t kill everything that has a potential danger in nature. Let’s keep some wildlife to enjoy!

Before talking about their potential danger, let me walk you through their life cycle.

Meet the caterpillar during different seasons:

Walking through nature in Spain or France, you might come across trees with dense dome shaped/tear drop shaped cocoons of what seems to be white candy-floss. Impenetrable as these nests are, they provide a safe place for processionary caterpillars, keeping them warm throughout the winter period, residing on the sun side of certain type of pine trees. The nest acts as a suntrap and the interior can reach over 20°C more than the outside. The caterpillars spend all day huddled together in the top of the nest, whilst their droppings accumulate in the lower part.

The “oak” moth variety (OPM) can be found on oaks, they can also be found in the occasional apple tree or palm tree.

PPM larvae hatch/emerge in autumn from the eggs laid in the summer, once pupated into lovely mothsn no longer causing problems, and begin feeding on the trees’ needles.These nocturnal caterpillars, forage in winter on pine needles (weakening the tree, but not causing its death) and return to their nest before daylight. A single colony can eat 2kg of needles, and it only takes 4 or 5 colonies for a 20year old tree to be denuded. In spring they become “processional”.


Although believed to be seen only from February until May, leaving their nest, forming endless nose to tail processions/conga lines, in search of soil to pupate a couple of months or even several years, mild autumns and winters could urge them to start walking as early as December. Ecologists use them as the basis for their studies on the effects of climate change, as these little ones benefit from global warming. They turn out to become a problem not only for the South but have extended their range to north of the Loire so only a few kms (20) away from Paris… Adults of both sexes can fly, and natural dispersal depends on the flight capacity of female moths, which is lower than that of males. Average female flying distance is 1.7km, with a maximum recorded of 10.5 km.

The adult moths live for only about a day in the summer, during which time they mate and lay eggs in pine trees.

Experiments in America have shown that if the caterpillars are put in a circle nose to tail, they will go round and round until they die from lack of food!

Their natural predators are: crested tits (eating the eggs and the very young caterpillars), the cuckoos (eating the caterpillars), the hoopoes (eating the pupa from the ground) and last but not least the bats (eating the moths).

Let’s tackle the worry now:

It might start with one nest in your surroundings, the following year there might be 3 or 4 more on the same tree, before spreading over the whole area (think 50 or more nests). The nests are situated at the very tops of the trees, about 40 to 50 feet high, so way out of reach in the topmost branches. Don’t touch the nests and you won’t encounter a problem at this stage, but once they start leaving the nests, they could be anywhere in your garden.

Many other caterpillars can cause skin irritation, but this particular species, and more specific their hairs, can cause a serious risk for young children, adults, dogs, horses, livestock. The hairs end in a sharp point that can bury into their victims like harpoons. The hair then bursts, liberating its toxin. And the hairs can be airborne. They contain “necro” and “neuro” toxins and are still virulent, even when the caterpillars are dead! The hairs’ highly allergenic protein (the irritating “taumetopein”) can, in humans, cause mild itching, even anaphylactic shock and infection of sensitive skin regions (mouth, nose, eyes).Often the effect is mild and passes quickly (especially if you take a hot shower).

To dogs / horses/ livestock, the caterpillars have a very bittersweet smell and taste, making the dog wanting to eat them, thus inhaling or absorbing their poison. Severe swelling and breathing difficulties, even necrosis of the tongue, will be the immediate result.

1processiondogmouthAs little as three or four of these caterpillars, will kill a medium sized dog.  That is where it becomes trickier.

There is no doubt, in case of possible infection, immediately clean the mouth of the pet with warm water and hurry to the vet. It is recommended that you keep anti histamine tablets handy as an early treatment. Homeopathic Apis pills can help to overcome the time before reaching the vet too. A dog`s or cat`s reaction on the nettle poison of the pine procession caterpillar: dreadful pain and itch, allergic shock, drop of blood pressure, extreme swelling of tongue as well as digestion an respiratory system, breathing problems, suffocation, apathetical behaviour, saliva and white foam from the mouth, asthmatic reaction, coma, kidney failure, death… Most small dogs die from contact with the poisonous caterpillar, some even within 1 hour!

A cortisone injection, repeated the next day will be the first treatment, amputating part of the tongue of your dog might be another action as it could wither and die, the dog´s tongue becomes neurotic and may fall off. There is no real anti-poison, but treatment with cortisone, blood pressure stimulants and pain-fighting medicine provide some relief and mostly rescue.

People should avoid the caterpillars’ habitat and dogs should be kept on a lead in nature. Basic rule: never walk unleashed dogs anywhere near pine trees.

But what if they show up in your garden…

Cutting down the infected branches or even trees that could lure them as habitat is one way of avoiding the danger.

Nests in trees, they should only be removed by professional contractors, as the irritant hairs could become airborne and you could breathe them in! Late summer, late afternoons (they can’t rebuild their nest during the day and will die unprotected in colder nights) are ideal to do that. In summer the caterpillars are still small,

What if they are walking on the ground?

None of the following actions seem very nice, but can save your pets. Use a weed burner, the flame guns for getting rid of weeds, and burn them where they are. It is always better than spraying insecticide (some local communities will get rid of them that way), as that will kill useful insects too and your dog might walk on it with its paws.

Pouring boiling water over the caterpillars will kill them but there will still be hairs floating down…

A pheromone trap attract the caterpillars and stop them from reaching the ground. Trapped in this pest control system, they can be transferred to less populated places or be eliminated more easily. This trap emits a hormone that makes all the male caterpillars smell like females, resulting in confusion, less babies and eventually the end of the colony. (http://www.exosect.com)

Eco-traps based on the same principle, avoiding them to reach the ground, are yet another solution.


Large plantations use a biological control, a bacteria (Bacillus thuringiensis ) is being aerially sprayed onto the trees to kill the caterpillars. To be affected the caterpillar must eat the bacteria, which produces a poison on exposure to the gut fluids. But this bacteria can kill many types of caterpillar, not just the target species, so it must be used in an informed and careful manner.

Hopefully this post has contributed to help owners take their responsibility for this threat to their pets in this part of France, an unfamiliar environment explained.

Life is not about waiting for the storm to pass, it’s about learning to dance in the rain.



1Pingbacks & Trackbacks on Lethal danger: The pine processionary moth’s caterpillar

  1. […] Vertaling artikel verschenen 01/03/2016 op woohoocuties.com, rechten uitsluitend voor Rescani, origineel artikel in het Engels te vinden op: http://woohoocuties.com/lethal-dangerthe-pine-processionary-moth/ […]

Leave a Reply

Your email address will not be published. Required fields are marked *

Comment *