Dogs & Killer Caterpillars – Pine Processionary Caterpillars

A hazard of which we were unaware until a friend living in Spain told us about it is the Pine Processionary Caterpillar. Awareness seems to be low and it was difficult to find information about the caterpillars, so I felt it would be useful to share my research here.

A second species, the Oak Processionary Caterpillar is also a hazard.

1. What is the Pine Processionary Caterpillar?
2. Where are the Caterpillars a Risk? 
3. When are the Caterpillars a Risk? 
4. Why is the Caterpillar a Risk? 
5. Preventative Advice 
6. Symptoms
7. Treatment
8. Further Information 
9. Oak Processionary Caterpillar
10. Useful? Pin It!
11. Disclaimer
12. Related
13. The Wuff Guide to Travelling with Dogs
14. Why Not Check Out My Bestselling Books?
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What is the Pine Processionary Caterpillar?

The pine processionary caterpillar is the larvae of a silk moth, Thaumetopoea pityocampa. They live ONLY in pine trees, feeding on the needles. Infected trees contain distinctive white nests, which look like cotton wool balls. Moving to burrow into the ground for the second (chrysalis) part of their life cycle, the caterpillars join up in long lines, nose to tail, which gives them their name. The caterpillars feed at night, and are most active between dusk and dawn.

Where are the Caterpillars a Risk? 

The caterpillars are natives of Southern Europe, Northern Africa, and parts of the Middle East. They were most common in Southern Europe (Spain and Portugal) but with climate change they have been moving north (click on the link for a map). There has been the odd sighting in France as far north as Paris. I don’t want to promote panic; we camped in a pine forest in Île d’Oléron in September and saw no sign of caterpillars, however a friend in Bordeaux did find and destroy an infected tree on his land.

The caterpillars are heat loving, so you will not find the nests at altitude, and they tend to be on the sunny side of the trees or forest.

When are the Caterpillars a Risk? 

The caterpillars are active in winter and spring, from around September to March or sometimes later, depending on location and weather conditions.It is simply a case of being informed and vigilant.

In Autumn, you will see the nests.

In Spring, the caterpillars emerge.

The caterpillars feed at night, and are most active between dusk and dawn, which is when you are most likely to see them.

Why is the Caterpillar a Risk? 

The moth itself poses no threat, but the caterpillars can cause harmful reactions in humans and animals and have been known to cause death in dogs.

The caterpillars protect themselves with a toxin (thaumetopoein) in the hairs around their body. The hairs inject the toxin, which can cause swelling, severe allergic reaction and anaphylactic shock.

A threatened caterpillar can fire its hairs like harpoons. Unfortunately, it’s not just a nosy dog poking around in the undergrowth and annoying a caterpillar that is at risk; the hairs don’t need to be on a caterpillar to cause a problem.

Hairs are shed in the nests and around infected trees, so even if the wind blows dust from under pine trees into your face or your pup walks on the litter under a tree and then licks his paws, it can mean trouble. According to some sources, shed hairs can still remain toxic for up to a year or more.

Preventative Advice 

Simply steer clear of infected pine trees – you will see the white nests.

September to May are times to be vigilant, although the caterpillars are not active throughout this period; it will depend on the climate and weather in the area where you are staying. The best advice is to ask locally. Sometimes, there may be warning signs, but don’t rely on this. We’ve never seen them!

I don’t want to promote panic. You ONLY need to worry about caterpillars in OBVIOUSLY INFECTED PINE TREES at the time of year WHEN THE CATERPILLARS ARE ACTIVE, although do note that in heavily affected areas, the toxic hairs can persist in leaf litter around infected trees.

Active caterpillars are easily spotted in their processionary lines, as in the picture above and the white nests are clearly visible in an infected tree.

If you have been in an infested area, wash your dog and wash the soles of your shoes so you don’t tread the hairs into your house or RV. Warm water helps deactivate the toxin.

Symptoms

The symptoms to look out for in your dog are:

• Drooling/Salivating
• Gagging/Vomiting
• Drowsiness/Listlessness
• Irritation (rubbing)
• Swelling of mouth, tongue or face
• Breathing difficulties – the severe swelling of lips and tongue can also cause breathing difficulties.
• Eye irritation/conjunctivitis.

If left untreated, infected tissue can die and fall off (necrosis) – our friend’s dog lost part of his tongue. I have a photo, but feel that it is a little too gory to post! A life-threatening allergic reaction to the toxin is also possible.

Treatment

If you see any of these symptoms, get to a vet immediately, particularly if you have been in an area with pine or oak trees. Prompt treatment will save your dog’s life

1. Washing your dog in warm water within the first two hours helps remove the toxin and contact with the stinging hairs. Heat inactivates the toxin, so a warm bath, or rinsing with warm water will help as a first line of action, but don’t delay seeking veterinary treatment.
2. Methylprednisolone, an anti-inflammatory steroid is one treatment indicated in cases of caterpillar toxicity, but this should be administered only under the care of a vet since dosages vary.
3. A homeopathic remedy, Apis is also suggested. As a scientist, I do have my reservations about homeopathy. Nevertheless, reports suggest that Apis helps as a first-line treatment against caterpillar toxins HOWEVER, do not let this deter you from seeking immediate veterinary treatment.

Further Information 

For a sanguine and factual account, click here. For more pictures of the caterpillars at all stages of development and an emotional story about a caterpillar encounter in Portugal, click here.

Oak Processionary Caterpillar

Another species of processionary caterpillar is the Oak Processionary Caterpillar. Also a native of Central and Southern Europe and the Middle East, unlike its Pine dwelling cousin, the Oak Processionary HAS been spread to the south-east of England and the Channel Islands, as well as northern Germany and the Netherlands, where it was either absent or rare previously. In heavily affected areas, it can move to other tree species, such as hornbeam, and is also worth avoiding.

In Britain, sightings should be reported through the Tree Alert in England, Scotland & Wales, or via the other means highlighted in the link. 

This link includes a list and map of countries affected by the Oak Processionary Caterpillar.

Photo attribution: Cover image of Pine Processionary caterpillars by Marc Pascual from Pixabay

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Disclaimer

Please note, I am a biochemist but not a vet, and have written this blog as a summary of my own research. As such, you use this information at your own risk. Although I make every effort to ensure that the information I provide is correct at the time of writing, things change all the time and it is essential that you always seek the most up to date advice from a qualified professional. Please see my Disclaimer page for more information.

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