WHAT DO YOU NEED TO KNOW ABOUT THE OAK PROCESSIONARY CATERPILLAR?

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Due to climate change, the oak processionary caterpillar is increasingly feeling at home in the Netherlands. Mild winters and dry hot summers encourage population growth. The shortage of natural enemies also means that the eggs and caterpillars are not eaten enough.

 

WHAT DO YOU NEED TO KNOW ABOUT THE OAK PROCESSIONARY CATERPILLAR?

WHAT IS AN OAK PROCESSIONARY CATERPILLAR?

The oak processionary caterpillar is the larva of the Thaumetopoea processionea, a moth. They can be recognized by the dense webs of molting skins, droppings and stinging hairs. The oak processionary caterpillar is one of the animal species that has benefited from climate change. The nuisance of the oak processionary caterpillar has increased enormously in recent years. Especially between mid-May and mid-July, oak processionary caterpillars cause many problems in the Netherlands and large parts of Europe.

The caterpillar has several molt stages. As young caterpillars they are still harmless, but after a few molts they develop stinging hairs. The caterpillars then have a woolly appearance: the shape most people know them from. They then turn into a harmless moth, which deposits clusters of eggs on oak trees and when these eggs hatch, the process starts all over again and the young caterpillars reappear.

IS AN OAK PROCESSIONARY CATERPILLAR DANGEROUS?

When humans come close to the caterpillar, they feel threatened. They then shoot off their microscopic arrow-shaped stinging hairs, with tiny barbs. The stinging hairs can be dangerous for humans and animals, they cause itching, respiratory problems, swelling or worse. In addition, the stinging hairs can in some cases cause serious allergic reactions. When your lips, tongue or eyelids get thicker and you start to feel stuffy, this usually means you’re having an allergic reaction. In that case, you should immediately contact your doctor.

WHAT SHOULD YOU DO IF YOU COME INTO CONTACT WITH THE STINGING HAIRS?

When you have come into contact with the stinging hairs, it is important not to scratch or rub, despite the enormous itching. Try to remove the stinging hairs from your skin with tape, but always use a ‘clean’ piece of tape. Rinse your skin carefully with lukewarm water and wash all worn clothing at at least 60 degrees. If you are not allergic, the symptoms usually go away on their own within 2 weeks.

WHY ARE WE SO BOTHERED BY THE OAK PROCESSIONARY CATERPILLAR?

Due to climate change, the oak processionary caterpillar is increasingly feeling at home in the Netherlands. Mild winters and dry hot summers encourage population growth. The shortage of natural enemies also means that the eggs and caterpillars are not eaten enough. The caterpillars that appear this year come from eggs deposited by the butterflies last summer.

Caterpillars can remain in the ground for a year or more until conditions are favorable enough to emerge. This makes it difficult to completely fight the caterpillar, because you don’t know where the caterpillars are all hidden. There are not enough beneficial insects to fight the caterpillars because there are fewer and fewer host plants on which they live. A host plant is a plant where beneficial insects feel comfortable and where they get their nutrition. In the Netherlands, we are increasingly choosing plants where beneficial insects do not feel at home and/or cannot get food. A combination of heat and insufficient natural enemies ensures that an infestation of the caterpillars arises every year.

THE SHORT TERM SOLUTION

Many municipalities choose, among other things, to suck out the nests with a special vacuum cleaner. The advantage of this is that the caterpillar with nest and all is sucked up. The disadvantage of this method is that not only the caterpillar is sucked up, but also part of the natural enemies. The larvae of the parasitic wasp and the parasitic fly often also live in the nests of the oak processionary caterpillar.

It is also possible that biological poison is sprayed on the leaves of the oak tree. Once the caterpillars eat these leaves, they die. And then there is also a method that uses nematodes, or small nematodes. These nematodes are sprayed on the nests and penetrate the body of the oak processionary caterpillar. There they leave bacteria behind, which then cause an intestinal infection that will kill the caterpillars. The disadvantage of these two methods is that not only the oak processionary caterpillars are killed, but also other caterpillars.

HOW CAN YOU ENSURE THAT THERE ARE FEWER OAK PROCESSIONARY CATERPILLARS IN YOUR OWN GARDEN?

In and through your garden or balcony you can also contribute to reducing the oak processionary caterpillar. Hang a nesting box for tits or nuthatches. Tits mainly eat young caterpillars and nuthatches even eat caterpillars with stinging hairs. Nesting boxes for bats can also be effective; bats like to eat the adult butterflies.

Native and wild host plants are a source of life and very important for attracting birds to your garden. Some host plants bear berries and other host plants attract insects. Birds love both of these! Flowering hedge plants such as the olive willow or the Portuguese cherry laurel are attractive. You should know that birds have a lot of red or blue-black berries, and less of white or yellow ones.

Besides the birds, the oak processionary caterpillar has even more natural enemies. The caterpillars are also eaten by larvae of lacewings, parasitic flies and parasitic wasps. As with birds, the following also applies here: native and wild host plants are very important to them. They prefer umbellate plants: hogweed, angelica and cow parsley.

THE LONG TERM SOLUTION

The long-term solution is a healthy cycle, we must help nature. A species-rich, more natural habitat helps to prevent the oak processionary caterpillar from gaining the upper hand. Birds, bats and insects can help keep numbers in check. We’ll have to help them with that.

In many places in the Netherlands there is still a lot to gain from natural control. There are very large areas of rural areas where an attractive landscape and biodiversity can ensure that the pest decreases. If the nature reserves are back in order, we will also have less trouble in the inhabited environment.

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