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Pine processionary caterpillar. Remedies, damages, and dangers

The pine processionary caterpillar is a highly dangerous insect to human health, animals, and trees. Here's how to eliminate it.

by BioGrow

Today, we want to focus our attention on the pine processionary caterpillar. A highly dangerous insect, especially for human and domestic animal health when unfortunately coming into contact with it. Learning to recognize this pine processionary caterpillar and keeping a safe distance is crucial.
When present on our trees, it is essential to understand how to intervene safely with biological treatments to eliminate it. One valuable ally in this regard is Bacillus thuringiensis.

In this article, we will see how to proceed and explain first aid procedures for humans and pets in case of accidental contact.

Thaumetopoea pityocampa

Pine processionary caterpillar larvae in a strict single-file line

Pine processionary caterpillar larvae in a strict single-file line

The pine processionary caterpillar (Thaumetopoea pityocampa) is a lepidopteran belonging to the family Thaumetopoeidae. The common name “processionary caterpillar” arises from the typical habit of the caterpillars moving in a strict Indian file, forming a sort of procession.
Defoliating larvae mainly attack pine trees, but also larches or firs, forming unmistakable and voluminous nests on these trees. This makes them easily recognizable to the careful observer.
The larvae measure about 30-40 mm and are hairy in the adult stage, with a black head and grayish body on the back. They also have ochre shades on the abdomen, while the back features a dense covering of reddish-brown hairs, giving the larvae a reddish-rusty coloration.
The adult processionary moths, with an approximate wingspan of 30/40 mm, have grayish wings with transverse brown streaks, resembling the bark of the plants they attack and on which they camouflage very well.

Biological Cycle of the Pine Processionary Caterpillar

Adult butterfly of the pine processionary

Adult butterfly of the pine processionary caterpillar

The pine processionary caterpillar larvae construct their nests, usually at the tips of trees or at the intersections of lateral branches. From there, they emerge at the beginning of spring, starting to feed on the leaves. The larvae are usually mature by the end of May, when they descend from the trees along the trunk. They move in typical processions and crawl on the ground where they bury themselves at a depth of a few centimeters. Then they pupate, keeping themselves at a short distance from the attacked plants.
Depending on the region, the larvae transform into moths from the beginning of summer until the end of July. During this period, mating and oviposition take place. The young larvae, in August, begin their damaging activity on the tree leaves and construct lighter nests. Towards the end of summer, with the approach of the cold period, they start building more compact nests. Inside these nests, they will overwinter until spring.
Therefore, this parasite completes only one generation per year.

Damages Caused by Pine Processionary Caterpillars on Pine Trees

Damage to vegetation caused by the pine processionary caterpillar

Damage to vegetation caused by the pine processionary caterpillar

The pine processionary caterpillar causes damage when it is in the larval stage. Adult moths, although annoying, do not cause direct problems. On trees, the damage varies depending on the age of the larvae and can be of different intensities.
Young larvae, which form during the summer, attack the needle-like leaves. After their attack, all that remains is a thread corresponding to the central vein of the pine needle. Subsequently, this vein necrotizes and withers, being used by the larvae to strengthen their nest.
Adult larvae, those that overwinter, are even more harmful as they eat the leaves completely, along with all the needles. They cause disastrous effects if the attack is massive. Moreover, if the attack is perpetuated over the years, the fate of the tree is complete withering and ultimately death.

Effects of Pine Processionary Caterpillars on Humans

Severe erythema caused by the pine processionary caterpillar

Severe erythema caused by the pine processionary caterpillar

Pine processionary caterpillar larvae require particular attention due to the direct damages they can cause to humans. The hairs covering the upper part of the larva are highly irritating as they contain histamine, a highly poisonous substance. These hairs are released by the larvae as a defense. They can detach due to wind action or fall from the nests. As we are mainly talking about pine, fir, and larch trees, which are often encountered in parks or woods during a walk, the battle against the processionary caterpillar is mandated by law by various public administrations.
The hairs of this insect have a particular microscopic hook shape and adhere very well to the epidermal zone. Human reactions vary depending on the extent and area of contact, ranging from a severe allergic reaction to an anaphylactic shock!


In case of skin contact, a severe skin rash occurs. This rash can easily spread not only to the directly affected area but also to the rest of the body through rubbing and sweating. Inhaling it causes respiratory tract irritation, leading to bronchospasm and breathing difficulties. Ingestion leads to inflammation of the mouth and intestines, accompanied by vomiting and abdominal pain. Eye contact results in rapid conjunctivitis, with severe cases possibly progressing to blindness.

What to Do

In case of contact, immediately seek medical attention for necessary medical treatment. Be careful not to rub the affected area as little as possible to avoid the spread of hairs. If the eyes are affected, rinse them immediately to remove any remaining hairs.
We recommend discarding your clothes as soon as possible. If you don’t want to throw them away, wash them separately from other garments at high temperatures while wearing gloves. You can understand the danger of this parasite.
Lastly, as a curiosity, some people may experience symptoms of entomophobia just by seeing the pine processionary caterpillar larvae perfectly organized in an Indian file.

Effects of Pine Processionary Caterpillars on Animals

The pine processionary caterpillar - damage on a dog's mouth

A wound on a dog’s mouth caused by the pine processionary caterpillar

The larvae of the pine processionary caterpillar are a danger not only to humans but also to animals. Dogs, as well as horses, for example, which are used to sniffing or eating grass, can come into contact with the irritating hairs of this insect and suffer severe damage.
The symptoms in dogs are quite common and begin with intense and abnormal salivation, caused by inflammation of the mouth. In case of ingestion, inflammation occurs, in a less severe form, also in the stomach and esophagus. Acute inflammation can progress rapidly, causing real burns and lacerations, in addition to swelling of the more affected parts of the animal’s mouth, which can lead to choking.
In such cases, the advice is to take the animal to the nearest veterinary center. In the immediate aftermath, you can perform a thorough mouthwash with a solution of water and baking soda. Be careful as the dog may act aggressively due to pain and shock, even if unintentionally.

Mechanical Removal of the Pine Processionary Nest

Pine processionary caterpillar mechanical removal

Mechanical removal of the pine processionary caterpillar nest

First of all, you can intervene mechanically by removing the nest. This operation is extremely delicate and very dangerous, so the operator must wear all possible personal safety devices (gloves, goggles, mask, protective suit) and must be cautious about the precarious balance on the tree vegetation. For this, ladders and appropriate handholds must be used.
Obviously, the operation can become progressively more problematic and often impractical due to the height of the tree. Once the nest is detached, along with the entire branch, it must be burned.

Mechanical Trap

A second technique involves the use of mass trapping traps that are purely mechanical. The trap is placed on the trunk of the tree and captures the caterpillars when they descend along the trunk in a procession to reach the ground and pupate, i.e., at the beginning of spring. Such a trap is quite effective and not too expensive.

Pheromone Trap

pheromone trap

Pheromone trap

Another type of trap for monitoring and mass capturing of pine processionary caterpillars is the pheromone trap. We have already encountered this type of trap in the fight against the tomato leafminer.
The pheromones simply reproduce the substances that the female emits to attract the male during the mating period, which is usually in the middle of summer. The trap serves a dual purpose: first, it is used for monitoring, and secondly, it allows the mass capture of the male to prevent reproduction and, therefore, the proliferation of the pine processionary caterpillars.
It should be positioned high to facilitate the entry of moths during their swarming. The pheromone should be replaced every 3 weeks.
It is important to note that this type of trap does not have any negative environmental impact, as it is entirely harmless to humans, plants, and other insects.

Bacillus Thuringiensis

In recent years, the use of Bacillus thuringiensis variety kurstaki, a biological insecticide we have already discussed in the past, has become widespread.
Bacillus thuringiensis is effective against the young larvae of the pine processionary caterpillar that form in August after the mating period. This is the best larval stage to successfully use this type of treatment.
Due to its effectiveness, low cost, and non-harmfulness to other animal and plant species, Bacillus thuringiensis is also used in large disinfections of wooded areas or parks carried out by competent public authorities. You can purchase this highly effective remedy here.
If you decide to carry out the treatment yourself, we recommend the same precautions as for the mechanical removal of the nests.

Predatory Insects

In nature, pine processionary caterpillars are controlled by various entomophagous insects. Even the State Forestry Corps, in its battle against the pine processionary caterpillar, has used them successfully.
Some of these insects, for example, include:

  • Xanthandrus comtus, predatory Syrphid fly
  • Erigorgus femorator, Ichneumon wasp
  • Tachinid flies
  • Formica rufa, lugubris, polyctena, aquilonia, predators of major forest defoliators
  • Chalcid wasps, parasitoids of eggs

Conclusion on Biological Defense

These are the techniques of biological defense. Unfortunately, there are also defense strategies that involve the use of heavy pesticides, one of which is inoculation, where a large and appropriate syringe is used to directly inject the phytosanitary treatment into the tree, affecting the pine processionary caterpillar but also poisoning the tree.
In conclusion, we repeat what we have already told you: be very careful in recognizing the pine processionary caterpillar. As you have read, it is a very dangerous insect. If you find it, take all necessary precautions.

Further Reading

  • Pine Processionary Caterpillar from SUNY Cortland: This resource discusses the pine processionary caterpillar, which is found in the warmer regions of southern Europe, the Near East, and North Africa. It is known for the habit of the caterpillars to move over the ground in a processionary manner.
  • Thaumetopoea pityocampa from Purdue University: This resource provides information about the pine processionary moth, also known as the pine processionary caterpillar, and stone-pine processionary caterpillar.
  • Pine processionary moth – Thaumetopoea pityocampa from Purdue University: This resource discusses the pine processionary moth (Thaumetopoea pityocampa), an insect pest of pine trees. This pest is active during cooler times of the year.

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