Researchers at the Oak Processional Caterpillar Knowledge Center have discovered that the caterpillars can sit in the ground for ten months without moving on to their next development phase. Then they come out, eat trees bare at a rapid pace and scatter stinging hairs around. In those cases, the caterpillars emerge from the ground in the fourth larval stage, with their dreaded stinging hairs.
If those hairs let go, they can be carried with the wind. And if people come into contact with those hairs, it causes irritation to the skin, airways and eyes. In severe cases, hospitalization may even be necessary. The most violent physical reaction is life-threatening anaphylactic shock. That is a sudden hypersensitivity reaction to an insect bite, for example.
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In the ground, the caterpillars can also pupate into butterflies, the researchers write on the platform Nature Today. The new insights make the fight against the caterpillars “a lot more complicated”, they write. “The caterpillars in the soil nests avoid the preventive spraying of oaks with nematodes and bacteria. The spraying is done earlier in the season.”
Too late for spraying
It is too late for spraying when the caterpillars come out full of stinging hairs in June. That means tree owners will also need to keep an eye on sprayed sites later in the year, the researchers say. They have to take into account that in some locations they still have to suck away caterpillars.
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In the knowledge center, the University of Wageningen, the RIVM and branch organizations of green companies work together. They also have good news: parasitic wasps and flies, natural enemies of the oak processionary caterpillar, can also go underground. “Stimulating natural enemies is therefore also an interesting option for soil nest control.”
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