What is the pine processionary?
The pine processionary (Thaumetopoea pityocampa) is a defoliating Lepidopteran considered the most damaging insect to Mediterranean pine forests. It is widely distributed throughout Southern Europe, Asia Minor, North Africa, and has also been introduced to various areas of South America. This species affects all native and exotic pines, as well as cedars and firs, being especially harmful in ecosystems where the Corsican pine, Scots pine, Canary Island pine, and exotic varieties such as Pinus radiata y Pinus ponderosa.
It receives different names depending on the region: pine processionary (Spain), cuc de pi (Catalonia and Valencian Community), foot bug (Balearic Islands), Sirganos (Teruel), piñu-mozorro (Basque Country), pine processionary caterpillar (Galicia) and furry cat (Argentina).
The caterpillars of this species are characterized by their social and gregarious behavior, forming large colonies that feed on the needles (leaves) of trees. The caterpillars possess stinging hairs They cause allergic reactions and irritations in humans and animals, making them a major public health problem in recreational areas, gardens, parks and areas with strong social use, especially from the third larval stage onwards.
Its importance lies both in ecological and productive damage —by causing defoliation that weakens the trees and makes them vulnerable to other pests and diseases— as in the health risks associated with contact with stinging hairs.
Morphology of the processionary caterpillar in its different phases
The pine processionary moth goes through a typical holometabolic cycle, consisting of egg, larva (caterpillar), pupa (chrysalis), and adult (moth). Each stage has its own morphological characteristics:
- Egg: The eggs are cylindrical and measure 4 to 5 cm in length. They are covered with scales from the female's anal tuft, resembling pine buds and serving as camouflage.
- Larva (caterpillar): Caterpillars go through five larval stages, differentiated by body color. They begin with a dull apple-green hue, then turn pinkish, reddish, and finally black with orange hairy bands on the back and white bands on the sides. In the third stage, they develop the characteristic reddish stinging hairs, which act as a defense mechanism against predators.
- Pupa (chrysalis): Pupation takes place underground, at a depth of about 10-20 cm, in oval, ochre-white silky cocoons that turn brownish over time.
- Adult (butterfly): The butterfly measures between 31 and 49 mm in wingspan, has ash-gray forewings and white hindwings with a dark anal spot. The body is hairy, and the male is usually smaller than the female.
These morphological differences in each phase allow the processionary caterpillar to be identified at any stage of its development.
Biological cycle of the pine processionary caterpillar
The life cycle of the pine processionary caterpillar is usually annual, although it can last several years depending on environmental conditions, especially at high altitudes or in cold climates, where the pupal phase can enter diapause.
- Egg laying: After mating at night, the female lays her eggs in a spiral around pine needles, preferably on peripheral, sunny shoots. Each clutch can contain between 70 and 300 eggs, protected by the female's scales.
- Hatching and larval development: Incubation lasts between 30 and 45 days. Upon hatching, the caterpillars gather in cooperative colonies and build small silk nests, which develop into visible nests or pockets on branches, serving as shelter from the low winter temperatures.
- Growth and formation of pockets: Caterpillars go through five developmental stages. From the third instar, they develop stinging hairs. They are most active and voracious in the fourth and fifth instars, where the consumption of needles can cause severe defoliation.
- Procession and burial: With the arrival of good weather, they often combine their movements into a "procession," descending from the trees in single file, led by a female, to bury themselves and pupate. They do so at a depth of 10-20 cm, where they form their chrysalides.
- Adult Emergency: Adult butterflies emerge after completing the pupal stage, although part of the population can extend this phase (diapause) for up to four years, especially at high altitudes.
Environmental factors that affect the processionary caterpillar
The development and distribution of the pine processionary caterpillar is strongly influenced by the climate:
- Very low temperatures (below -12 ºC) can kill entire colonies.
- High rainfall It makes reproduction difficult and reduces the incidence of the pest.
- Optimum activity temperature: Between 10 and 20°C, the caterpillars are active, although growth slows. Above 30°C, the colonies disintegrate, and above 32°C, the larvae may die.
- Humidity of floor: It is crucial for the hatching and proper development of buried pupae.
- Activity thresholds: On cold nights, caterpillars may come out to feed during the day.
Climate change, resulting in milder winters and warmer springs, may favor the proliferation and geographic expansion of the processionary caterpillar.
Damage caused by the pine processionary caterpillar
The processionary caterpillar is considered the most important defoliator in Mediterranean pine forests. Its damage can be divided into:
- Direct damage to trees: The caterpillars feed on the needles. In the early stages, damage is mild, with yellowish needles with silken excrement visible. In advanced stages, the needles dry out and fall, resulting in partial or complete defoliation. This weakens the tree, slows its growth, and predisposes it to other pests and diseases.
- Cumulative damage: With successive infestations, the weakening increases, compromising the pine's ability to survive drought, fungal attacks, and other insects.
- Forest and productive impact: It can cause significant losses in forests and plantations, reducing their timber, ornamental and reforestation value.
On rare occasions, even after several consecutive defoliations, adult pines die, but their vigor steadily declines.
Pine processionary moth: dangers to human and animal health
The main health risk of the processionary caterpillar lies in the stinging hairs that develops from the third larval stage. These hairs contain a heat-labile toxin called Thaumatopin and can become detached, floating in the air and causing various illnesses in people and animals.
- People: Contact with stinging hairs causes hives, dermatitis, irritation of the eyes, nose and throat, conjunctivitis and, in sensitive people, severe allergic reactions or even anaphylactic shockChildren are especially vulnerable. Simply passing near nests or caterpillars can trigger symptoms, even without having to touch them directly.
- Domestic animals: Dogs are the most affected, as they often sniff the ground and may lick or bite abandoned caterpillars or nests. This can cause swelling of the muzzle, tongue, and throat, vomiting, fever, conjunctivitis, and even necrosis in affected areas. Inhalation can cause fatal asphyxiation If the airways become inflamed, it is essential to see a veterinarian immediately if contact is suspected.
Recommendations to avoid problems are:
- Do not touch the caterpillars or the bags., nor allow children or pets to approach.
- In case of contact, wash the affected area with warm water and seek medical or veterinary advice immediately.
- Avoid walking through affected areas during the months of greatest larval activity.
Symptoms of poisoning or allergy by processionary caterpillars
- In humans: Itching, swelling, redness, and blistering if the hairs are in contact with the skin; watering and drooping of the eyelids if there is eye contact; sneezing, coughing, and sore throat if the hairs are inhaled.
- In dogs: swelling of the muzzle and tongue, excessive drooling, respiratory difficulty, fever, fatigue, vomiting, necrosis of the tongue or mucous membranes, conjunctivitis, and possible suffocation.
If any symptoms appear, it is important to wash the affected area and seek medical or veterinary care immediately.
Processionary moth: ecological risks and role in the ecosystem
The pine processionary caterpillar is a native species in Mediterranean ecosystems. It is fully integrated into the trophic web and constitutes food in all its phases for a wide variety of predators (eggs, caterpillars, pupae and adult butterflies):
- Insectivorous birds: blue tits, coal tits, cuckoos, hoopoes, magpies, crows and thrushes.
- Mammals: bats, dormouse.
- Insects: red ants, wasps, orthopterans, predators and parasitoids of eggs (Ichneumonidae, Braconidae) and larvae (Tachinidae).
- Soil organisms: fungi of the genus Cordyceps that infect pupae, viruses and pathogenic bacteria.
Natural biological control is essential for the population balance and, except in cases of extreme proliferation, it is the most sustainable and recommendable method.
Why is it not advisable to consider the processionary caterpillar as an external pest?
Although it can cause significant damage, the processionary caterpillar is not an exotic pest, but rather part of the natural ecological balance of forests. The defoliation it causes rarely kills adult pines except under stressful conditions or under repeated attacks. The real danger lies in its stinging nature and the damage it causes in urban or recreational areas.
How to control and combat the pine processionary caterpillar?
Processionary caterpillar management requires an integrated approach, combining natural and artificial methods:
Natural and biological control
- Promotion of auxiliary fauna: Encourage the presence of insectivorous birds by placing nesting boxes, maintaining hedges and diverse vegetation, and not eliminating natural predators.
- Entomopathogenic fungi: Cordyceps and other soil fungi infect pupae and reduce adult emergence, especially during burial and in moist soils.
- Parasitoids and predators: Protection from wasps and ants helps reduce the survival of eggs and larvae.
Physical and mechanical control
- Elimination of pockets: Cut and burn nests when the caterpillars are inside, preferably on cool days and at dusk. It is advisable to water them beforehand to reduce the risk of dispersing the stinging hairs. This work must be performed by trained and protected personnel.
- Methods for capturing descending caterpillars: Place helical rings or plastic funnels on the trunk to catch caterpillars as they move to the ground. The funnel can be filled with water to eliminate the caterpillars.
- Detection and removal: Locate nesting areas. If the caterpillars are buried, a mound of disturbed soil can be seen; in gardens, it should be dug up and removed manually.
Pheromone control
- Sex pheromone traps: They are used to capture adult males during the butterfly's flight period, reducing copulation and, consequently, egg laying. They are especially useful for population monitoring and predicting larval emergence.
Chemical and microbiological control
- Chemical treatments: Based on authorized insecticides (pyrethroids, chitin inhibitors, diflubenzuron or Bacillus thuringiensis). They should be applied only in the early larval stages and by terrestrial means. Treatment should be reserved for severe cases and carried out in the fall, avoiding harming other beneficial insects.
- Aerial spraying: Currently banned in most European Union countries to protect biodiversity and reduce environmental pollution.
- Trunk injection: In urban areas, some municipalities apply an injection into the trunk to deliver the insecticide intravascularly, acting directly against the pest.
Preventive measures and silvicultural recommendations
- Selection of species in reforestation: Avoid replanting highly sensitive species such as black pine or exotic pines in at-risk areas. Diversifying species improves forest resilience.
- Annual monitoring and follow-up: Monitor the presence of pockets and caterpillars, establish control areas, and respond to population damage thresholds.
- Management of the environment: Carry out thinning and pruning to allow light and ventilation.
Specific measures in public areas, parks and gardens
In public areas, gardens and parks, vigilance and prevention must be extreme:
- Signaling and delimitation of infested areas during the caterpillar descent season.
- Information campaigns for the population and pet owners.
- Regular cleaning of pockets and caterpillar debris by qualified personnel.
The use of pheromone traps, controlling descending caterpillars, and promoting urban biodiversity are essential practices.
When to act against the processionary caterpillar?
Control is most effective in the first larval stages, just after the eggs hatch and before the caterpillars develop stinging hairs (third instar). Biological and chemical treatments should be scheduled at this stage to maximize effectiveness and minimize risks.
Monitoring with pheromone traps and direct observation of pockets allows determining the optimal time for intervention.
Innovations and citizen monitoring projects
Currently, initiatives such as ForestAlert They promote citizen participation to monitor the processionary caterpillar and other forest problems. Mobile applications and photographs can provide valuable information on the health of pine forests.
A thorough understanding of the pine processionary moth's life cycle, impact, control measures, and ecological role is essential to addressing the problem effectively, responsibly, and sustainably. Maintaining the balance between health risk management and ecosystem preservation requires integrated interventions, up-to-date information, and the collaboration of all members of society.
