Chickadees, a natural remedy against processionary caterpillars

A blue tit in a fruit tree, in Alsace, in 2008.

“You have to look up to see themsaid with a smile Yannick Andres, head of the tree service of the town hall of Nancy, pointing to a birdhouse. It’s starting to get busy. » To fight against the proliferation of processionary caterpillars in the city, the agent contributed to the installation, in January 2021, of around fifty nesting boxes for tits in Sainte-Marie Park. A discreet little bird with a devastating appetite, the tit loves larvae and seems to like the tops of Nancy trees.

By inviting tits – great or blue – to settle permanently, Yannick Andres tries to restore a balance between invasive caterpillars and birds mistreated by the urbanization of their natural environment. “The tits settle in at the first spawning, when they need to feed the young, in the middle of May, and there they are a hit”, explains the agent. A pair of tits can devour up to 500 caterpillar larvae per day to feed their young.

Oak and pine processionary caterpillars proliferate on French territory. In Nancy, it is that of the oak which poses a problem. Unlike that of the pine, it does not move in single file, but nests in the trees and deposits its stinging hairs in its nest before its moult. Sandra Sinno-Tellier, medical epidemiologist at the National Agency for Food, Environmental and Occupational Health and Safety (Anses), monitors the expansion of the two species. “Between 2012 and 2019, there was a steady increase in the number of calls to poison control centers for poisonings linked to the oak processionary caterpillar”says the scientist.

So much so that the processionary caterpillar of the pine and that of the oak were classified, by a government decree of April 25, “species whose proliferation is harmful to human health”which makes it possible to multiply the measures to combat their spread.

Micro-harpoons

Each year, most cases are recorded between January and April for the pine caterpillar, while those linked to the oak caterpillar are concentrated between April and July. Covered in volatile stinging hairs, the caterpillars shed their cover in the event of external aggression. A fearsome defense mechanism, toxin-laden hairs can cause serious inflammatory reactions in humans. The toxic protein contained in the hair can cause skin, eye, digestive and even respiratory damage. Very light and invisible, these micro-harpoons can be stored in empty nests for months and released by a gust of wind. Thus, many patients develop symptoms without ever seeing a caterpillar.

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