The processionary caterpillars resurface and move in long Indian queues in our parks, gardens and forests.
PIN processionary tracks (Photo Chenille-risque.info)
If their procession fascinates, their danger is very real : Their stinging hairs can cause irritation and respiratory problems, and are a serious threat to domestic animals.
THE processionaries Pin (Thaumetopoea Pityocampa) leave the nest to burst underground: it is the nymphosis procession, a period during which the caterpillars are particularly dangerous for humans and animals because they are at ground level.
According to Météo-France, the fall of 2023 has ranked first in the hottest autumns since 1900 in front of the 2006 and 2022 autumn (+2.1 ° C). Indeed, the tracks of processionaries of the pine need precise thermal conditions to eat: they can only eat if it is more than 9 ° C in their nests during the day and more than 0 ° C in the air at night .
Due to climate change, these early processions observations will be more and more usual. Indeed, according to Météo-France, the evolution of the climate leads to increasingly mild winters. Over the past 15 years, we have measured four of the five hottest winters in history, in 2007, 2014, 2016 and 2020.
PIN processionary tracks (Photo Chenille-risque.info)
This year, due to the overall favorable weather, many caterpillars are starting this month of February throughout the territory.
The stinging hairs found on the caterpillars (even dead), in nests (even empty) and in landfill are dangerous for humans and domestic animals. They can cause various reactions: irritation of the respiratory tract, eruptions with itching, conjunctivitis, inflammation of mucous membranes (animal language).
The hair is very volatile and can easily hang on on clothing or hair and animal hair while keeping their potential stinging, even for several years.
To protect yourself? Wear long clothes, rinse your clothes and hair and your animals' hairs when you get in walks. Avoid risk areas during the caterpillar presence period.
During their larval stage, pine processionaries feed on trees. In a Scientific article published in 2012researchers have been interested in the impact of these defoliations on the growth of trees, with the aim of better understanding their long -term effects and their influence on the ability of forests to kidnap carbon, a key factor in the fight against Climate change.
- PIN processionary tracks (Photo Chenille-risque.info)
The researchers conducted an in -depth study by analyzing the data from 45 case studies, in order to compare growth between defoliated and witnesses. The defoliations caused by processionary caterpillars cause an average loss of 43 % of the growth of affected trees.
The results show that the higher the rate of defoliation, the greater the loss of growth, reaching approximately 20 % for low defoliations (5-24 %) and almost 50 % for severe defoliations (more than 50 %). However, the effect seems to stabilize beyond 50 % of defoliation.
The analysis of the data reveals that young trees are experiencing more marked growth losses than their older counterparts. This observation is particularly obvious in low (5-24 %) and very high (75-100 %) classes.
According to the article, young trees are more affected by the defoliations caused by processionary caterpillars because they are in the active growth phase. This means that they need more energy to grow and develop, which makes them more vulnerable to the loss of foliage.
When they are defolved, they lose a large part of their needles, which reduces their ability to do photosynthesis, and therefore produce the energy necessary to continue to grow. In comparison, older trees have already reached a more stable size and depend less on the rapid production of biomass. Their more developed root system gives them better resistance to disturbances.
The black pines of Austria serve as nursery for processionary caterpillars • François Desmeures
These growth losses are particularly worrying in the context of climate change, as they can decrease the capacity of forests to kidnap carbon. Indeed, when the growth of trees slows down, their ability to absorb and store carbon dioxide (CO2) decreases, which could worsen the effects of global warming.
The results of this study highlight the importance of integrating the impact of defoliations in forest management models, especially in regions where the processionary caterpillar is widespread. Researchers recommend monitoring the populations of processionary caterpillars carefully and developing suitable control strategies to limit their impact on forests.
Sources : Jacquet, J. S., Orazio, C., & Jactel, H. (2012). Defoliation by processionary moth significantly reduces tree growth: a quantitative review. Annals of forest science, 69, 857-866. https://doi.org/10.1007/s13595-012-0209-
