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Processionary caterpillars in the UK: Health risks for dogs

yellow labrador walking through forest

Processionary caterpillars are most active during the spring and are very dangerous for dogs

© Au_Cr - Shutterstock

While they may look harmless, processionary caterpillars can be extremely dangerous for our pets, and in the worst cases, fatal. Here’s what you need to know about them.

By Justine Seraphin

Published on the

Processionary caterpillars are the larval stage of a type of moth. While the moth itself is harmless, the caterpillar has urticating hairs that can be very dangerous for dogs, cats, and even humans.

Processionary caterpillars are particularly active during the spring, so now’s the time to learn about them! Here’s everything you need to know about processionary caterpillars: 

What are processionary moth caterpillars?

Processionary moths lay eggs at the tops of oak trees and pine trees. Their eggs hatch in spring and early summer. The caterpillars then travel down from the tops of the trees to the ground, where they will burrow until they emerge as a fully grown adult moth. The caterpillars travel in a characteristic nose-to-tail fashion, which is why they’re known as “processionary”. 

While the moths are harmless, the caterpillar stage is very dangerous to humans and animals. Indeed, processionary caterpillars are covered in hairs that contain a urticating protein called thaumetopoein, which can provoke serious allergic reactions, and in the worst of cases, death. While direct contact with the caterpillar is most likely going to cause a serious reaction, symptoms can also occur if there has been contact with a fallen nest or a volatile caterpillar hairs.

Are there processionary caterpillars in the UK?

Oak and Pine Processionary caterpillars are very common throughout southern Europe, particularly in France and Spain. 

In the UK, only Oak Processionary Moth (OPM) caterpillars have been reported. They are increasingly present in London, Berkshire, Buckinghamshire, Essex, Hertfordshire, and Surrey. 

Processionary caterpillars: What are the risks for dogs?

Dogs are particularly at risk of being in contact with processionary moth caterpillars because they are curious creatures who like to sniff and lick anything in sight. During the spring, the caterpillars are traveling from the trees to the ground, and so, are likely to cross paths with humans and animals on their way down. 

Simply sniffing a nest or caterpillar is likely to cause inflammation and discomfort for your pet. Licking or ingestion can have much more serious consequences, such as necrosis of the tongue and damage to the digestive tract. If left untreated, it could even lead to death.

Symptoms of contact with processionary caterpillars

If your dog has been in direct contact with a caterpillar, you may notice one or several of the following symptoms:

  • Swollen tongue, mouth, eyes or affected area
  • Skin irritation and appearance of rashes
  • Diarrhoea
  • Loss of appetite
  • Excessive salivation 
  • Difficulty breathing or gagging
  • Vomiting
  • Fever

Treatment for a dog who’s been in contact with a processionary caterpillar

Your priority should be to remove any hairs that may be inside your dog’s mouth. To do so, put on some thick gloves, then pour some water or a baking soda/water mix into their mouth. Do not scrub, as this could make things worse. 

Next, take your pet to the emergency vet. The sooner your pet receives treatment, the less likely it is to develop a serious reaction.

How to avoid contact with processionary caterpillars

If you live in an area that is likely to be home to processionary caterpillars (e.g. London, Berkshire, Buckinghamshire, Essex, Hertfordshire, and Surrey), be particularly careful during the spring and summer. Avoid walking your dog in heavily wooded areas, and particularly in pine forests or areas with a lot of oak trees. Practice recall with your pet so you can call them back to you easily if they start sniffing something you’re not familiar with. And if your dog is hopeless at recall and an avid eater of just about everything, then you might want to try putting a basket muzzle on them during walks.

Pay close attention to your dog if you take forest walks during the spring! ©Wamiz

Remember to always report sightings of processionary caterpillars - you’ll be helping other dog owners around the UK!

Frequently asked questions

Can I inject my dog after contact with processionary caterpillars?

Is it bad if a dog eats a caterpillar?

How do you get rid of processionary caterpillars?

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