How Dangerous Are Portugal’s Processionary Caterpillars?

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Written by: | Last updated on January 25, 2024 | Est. Reading Time: 5 minutes
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If you’re moving to Portugal, one insect you’ll hear a lot about is the processionary caterpillar or pine processionary caterpillar. But what are these creatures and why are people so concerned about them? After all, they’re just a caterpillar, right?

How dangerous are these to humans?

The hairs of these caterpillars contain an irritating toxin which can cause significant allergic reactions in humans and animals. Contact with these hairs, often airborne, can result in skin rashes, eye irritations, and breathing difficulties. This poses a particular risk in areas frequented by children, pets, and those susceptible to allergies. 

In most cases, the biggest danger is to pets, particularly dogs, and also children. However, adults can be affected too, although it seems to depend on the particular adult. 

In 2023, Hollywood star Jamie Dornan experienced a harrowing encounter with these venomous caterpillars, necessitating a hospital visit. This incident was shared by his friend, Gordon Smart, who also required medical attention.

Smart recalled being the first among the group to exhibit alarming symptoms, such as a tingling sensation in his left arm and hand. Concerned, he discreetly headed to a medical centre, leaving his three friends behind under the apprehension that he might be suffering from a heart attack.

At the medical centre, Smart was informed that his heart rate had skyrocketed to 210 beats per minute. For context, the British Heart Foundation states that a normal resting heart rate typically ranges from 60 to 100 beats per minute. Following this diagnosis, he was promptly sent to the hospital in an Uber.

As mentioned, the seriousness to humans depends on the individual. 

How dangerous are these to pets?

Dogs, in particular, are prone to distress if they inadvertently come into contact with the hairs shed by these caterpillars. This situation can quickly escalate if the dog sniffs or ingests a caterpillar. The fine hairs can cause severe damage, potentially leading to the necrosis of the tongue, esophagus, and stomach. 

A common reaction involves immediate discomfort, leading to incessant licking of their paws. Symptoms often include excessive drooling and saliva production, chomping, and white spots on the tongue. 

In extreme cases, dogs have been known to suffer significant damage to their tongues, and may even lose them, due to this contact. The risks extend to cats as well, with ingestion of these caterpillars potentially proving fatal. 

It is crucial to seek veterinary assistance without delay if your pet encounters processionary caterpillars. Prompt and urgent veterinary care is essential in these situations.

When Are They In Season?

Like most caterpillars, these creatures develop in distinct stages, namely:

  • Egg
  • Caterpillar
  • Pupa or Chrysalis (Cocoon)
  • Adult Insect (Butterfly)

These caterpillars experience five stages of growth during the caterpillar stage. Starting from their third stage, they develop the stinging hairs, which are known to trigger allergic reactions, affecting the skin, eyes, and respiratory system.

Depending on the weather that year, amongst other factors, you’ll normally spot these caterpillars between the months of January and April. However, some people have spotted them in December as well. 

They seem to be more common in the Algarve and the rest of Southern Portugal, however these beasties have been spotted as far North as Paris. Increasing temperatures as a result of climate change could see more of them in the rest of Portugal. 

How to Spot Them?

processionary caterpillar nest
© DepositPhotos

It’s easy to spot these caterpillars when they’re on the ground because they form a procession or line. 

When inspecting pine trees for nests, direct your look towards the top; a single tree can host multiple nests. In smaller pine trees, these nests might be at or near eye level.

Dealing with them

For those with pine trees on their property, considering the removal of these nests is advisable, and in some cases, it might be prudent to remove the pine trees entirely. There are numerous professional services available that specialise in safely removing and disposing of these nests.

Some people recommend not dealing with these yourself in case the hairs become airborne. For those that wish to, Safe Communities Portugal has some helpful advice.

You should:

  • Try to catch them as they come down the trunk by taping them, over a length of 0.50 m to 1 m, with
    plastic or paper soaked on both sides with odourless poly-solbutadiene-based glue;
  • On the ground, gather them together with the help of a rake, gardening broom or any other similar
  • Burn or crush them gently so as not to cause the projection of hairs as a defensive reaction;
  • If it is possible to identify the burial site, which is usually in a sunny area in cold and temperate
    climates or near the original trees in warmer climates, dig the soil to expose the pupae that have
    already formed or the caterpillars that have managed to bury themselves. Depending on the soil
    texture the depth varies up to a maximum of 10-15 cm.

When carrying out any of the recommended treatments, you should:

  • Wear gloves;
  • Protect the neck;
  • Protect the eyes by wearing suitable goggles;
  • Wear protective nose and mouth mask;
  • Follow the application safety rules on the labels of each product.
Written by

James Cave is the founder of Portugalist and the author of the bestselling book, Moving to Portugal Made Simple. He has visited just about every part of Portugal, including Madeira and all nine islands of the Azores, and lived in several parts of Portugal including Lisbon, the Algarve, and Northern Portugal.