Processionnaire du pin : expansion vers le nord due au réchauffement climatique

European forests are facing an unprecedented ecological crisis as oak processionary moth (*Thaumetopoea processionea*) outbreaks reach record levels, with infestations expanding rapidly northward due to climate change. Scientists warn that the caterpillars’ hairy nests—filled with venomous urticating hairs—pose severe risks to both ecosystems and human health, threatening biodiversity, timber industries, and public safety across the continent.

The oak processionary moth, long established in southern Europe, has now spread aggressively into central and northern regions, including Germany, Belgium, and even parts of the UK, according to the European Commission’s Plant Health Directorate. While historically confined to Mediterranean climates, rising temperatures and shifting rainfall patterns have created ideal conditions for their proliferation. “We’re seeing infestation levels that are 30–50% higher than the five-year average in affected regions,” states Dr. Markus Riecken, an entomologist at the Thünen Institute for Forest Ecosystems in Germany. “This isn’t just a local issue—it’s a continental-scale problem.”

The moth’s larvae, recognizable by their distinctive processionary movement, spin dense silk nests on oak trees that can measure up to 30 centimeters in diameter. These nests harbor thousands of urticating hairs, which break off easily and can cause severe skin irritation, respiratory issues, and even blindness if they come into contact with eyes. Health authorities in France and Spain have reported a 40% increase in allergic reactions tied to the caterpillars since 2020, with hospitals in southern France treating dozens of cases annually during outbreak seasons.

The economic toll is equally alarming. Oak trees are vital to Europe’s timber industry, supporting everything from furniture manufacturing to cork production. A 2023 study by the European Environment Agency estimated that oak processionary moth infestations could cost the EU economy up to €1.2 billion annually in lost timber revenue and increased pest-control measures. “This isn’t just about losing trees—it’s about losing entire ecosystems,” warns Dr. Riecken. “Oak forests support hundreds of species, from birds to fungi, and their decline could trigger cascading ecological consequences.”

Why Are Oak Processionary Moth Outbreaks Worsening?

Climate change is the primary driver behind the moths’ northward expansion. Warmer winters reduce mortality rates among overwintering larvae, while increased rainfall creates ideal conditions for oak tree health—providing more food for the caterpillars. Research published in Global Change Biology found that regions experiencing temperature increases of just 1–2°C have seen infestation rates rise by up to 60% over the past decade.

Another critical factor is the lack of natural predators in newly affected areas. While birds and wasps help control populations in southern Europe, northern regions have yet to develop these ecological checks and balances. “The moths are essentially moving into a vacuum where they face no resistance,” explains Dr. Elena Sánchez, a forest ecologist at the Spanish National Research Council (CSIC). “This creates perfect conditions for explosive population growth.”

Human activity has also played a role. The increased movement of firewood and oak products across Europe has accelerated the moth’s spread, with infestations now reported in non-native oak species planted for landscaping. The European Food Safety Authority (EFSA) has classified the oak processionary moth as a “high-risk” invasive species, urging stricter quarantine measures on imported plant materials.

How Are Authorities Responding to the Crisis?

European governments and scientific bodies are deploying a multi-pronged approach to combat the infestations. Biological control methods, such as introducing natural predators like the Bracon niger wasp, are showing promise in pilot programs. France has already treated over 50,000 hectares of infested forest using pheromone traps and bacterial sprays, while Germany is testing drone-based pesticide applications to target large-scale outbreaks.

Public health measures are also being strengthened. The World Health Organization’s Regional Office for Europe has issued guidelines urging residents in affected areas to avoid oak trees during outbreak seasons, particularly in spring and autumn when caterpillars are most active. “We’re seeing a real public health emergency in some regions,” states Dr. Hans Kluge, WHO regional director. “People need to be aware that these hairs can remain airborne for days and cause severe reactions.”

At the policy level, the European Commission is pushing for mandatory reporting of oak processionary moth sightings across member states, with plans to establish a continent-wide early warning system by 2025. The EU Plant Health Regulation, updated in 2021, now includes stricter controls on the movement of oak wood and nursery stock to prevent further spread.

What Are the Long-Term Ecological Risks?

Beyond immediate health and economic impacts, scientists warn of long-term ecological consequences. Oak trees are keystone species in European forests, supporting over 1,500 dependent species, including endangered birds like the Turdus merula (song thrush). Large-scale oak die-offs could disrupt entire food chains, with ripple effects on mammals, insects, and fungi.

There are also concerns about genetic contamination. While the oak processionary moth primarily targets native oak species, there is growing evidence that it can adapt to feed on related species like chestnut and beech trees. “If this happens, we could see these infestations spreading to entirely new ecosystems,” cautions Dr. Riecken. “The stakes couldn’t be higher for Europe’s forests.”

Climate models suggest that without intervention, oak processionary moth populations could expand into Scandinavia and the Baltic states within the next 20 years. “This is a classic example of how climate change accelerates invasive species,” notes Dr. Sánchez. “The moths are just the first wave—other forest pests are likely to follow as temperatures continue to rise.”

How Can the Public Protect Themselves?

Residents in affected areas can take several precautions to reduce risks:

• Avoid oak trees during outbreak seasons (typically spring and autumn). The caterpillars are most active during these periods.
• Wear protective clothing when near oak trees, including long sleeves, gloves, and goggles to prevent hair contact.
• Report sightings to local agricultural authorities. Many countries have dedicated hotlines for pest reporting (e.g., France’s Signalement Végétal platform).
• Clean pets thoroughly after walks in wooded areas, as their fur can carry urticating hairs.
• Monitor for symptoms such as skin rashes, respiratory difficulties, or eye irritation, and seek medical attention if exposed.

For those living near infested forests, the European Environment Agency recommends installing fine-mesh nets around outdoor furniture and play areas to prevent hair accumulation. “Prevention is key,” advises Dr. Kluge. “The more we can slow the spread of these infestations, the better we can protect both people and ecosystems.”

What Happens Next?

The next critical checkpoint is the European Commission’s 2025 Plant Health Strategy Review, scheduled for June 15, 2025. This meeting will assess the effectiveness of current containment measures and may introduce stricter cross-border regulations on oak products. Meanwhile, field trials for biological control methods will continue through 2024, with preliminary results expected by next spring.

For the latest updates on oak processionary moth activity, residents can consult:

• EU Plant Health Portal
• ANSES France (Health Risks)
• Thünen Institute (Germany)
• WHO Europe (Public Health Alerts)

Frequently Asked Questions