When you see colorfully dressed types chasing after each other, you probably think of a polonaise. Me too. And immediately afterwards I naturally think of a procession of oak processionary caterpillars, Thaumetopoea processionea.
Oak processionary caterpillars move in procession, hence their name. They follow each other on their way to the next drink, not a glass of beer, but an oak with fresh leaves. Oak processionary caterpillars go head to ass. The animals follow the scent of their congeners, but they mainly follow another when they are stimulated by hairs at the back of the predecessor.
The caterpillars like to socialize. They feel comfortable in a group. They celebrate their party at a time of year when the temperature is a lot more pleasant. Around early May, right after they hatch, they sit together at dusk, nibbling on oak leaves and buds in the tops of the trees. During the day they all sleep in a tent made of silk threads. At the beginning of their lives, such a tent does not catch the eye at all and it looks a bit like a spider’s web in the shadow.
At that very beginning, we don’t notice those creatures yet. They are small, hidden and have no stinging hairs yet. These only arise after the oak processionary caterpillars have moulted three times. Between their long, white hairs, the animals have dark, velvety patches on the top of their bodies, which contain tiny hairs. They are released when the caterpillars have to defend themselves. With their arrow shape, the fire hairs move easily through the air, after which they can anchor themselves firmly in the skin with tiny barbs. The poison in the hairs can then cause an allergic reaction with a severe itchy skin rash, painfully inflamed eyes and even breathing problems.
By then we will notice oak processionary caterpillars. They are therefore much more visible and can hide in large tents around branches or on tree trunks. And they therefore cause irritation, even if they are not running a polonaise.
When the fun ends, the caterpillars stop eating. They take off their attire of savage, long hair on orange-red warts. In this way they also get rid of the hidden fire hairs. Under the old skin is a doll skin, in which they undergo their metamorphosis. The creatures that some people are allergic to disappear. What then appears in early July are modest-looking grey-brown moths with downy soft hairs on the legs and thorax. They don’t run a polonaise. They do flirt with each other. We know what comes of that. Itch.
A version of this article also appeared in NRC Handelsblad on 5 March 2022
A version of this article also appeared in NRC in the morning of March 5, 2022
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