This summer, the oak processionary caterpillar caused a big kerfuffle, as its numbers grew three-fold in most places in the Netherlands and many people suffered from the effects the stinging hairs can have.

Reducing the caterpillar population

Many people suffered from itchy skin after contact with the oak processionary caterpillar’s stinging hairs and more than 100 people experienced serious eye problems. Many municipalities only tackled the caterpillar problem after complaints from residents and in many cases, the insects were vacuumed up and destroyed in a waste incinerator. 

This time around, municipalities are turning to nature to tackle the pesky caterpillar. To be precise, dozens are going to transform their tree stock, for example planting other species when trees are removed due to old age or sickness, so that there are fewer oak trees. Additionally, an increasing number of municipalities are looking into fighting the pest with natural predators and others into organic pest control, according to a survey by NOS.

Encouraging natural predators

Experts believe it’s better to tackle the oak processionary caterpillar by lending its natural predators a helping hand. This is an idea which is receiving a bigger and bigger following. By stimulating the populations of birds, bats and insects which prey on the pesky caterpillar, the population of the pest will be reduced. Methods for attracting more of these predators are quite simple, ranging from having more wildflowers on roadsides to hanging up breeding boxes for great tits.

Amersfoort is one of the municipalities going for the natural predator approach. Trials using natural methods have begun in four different locations in the municipality. These trials will last three years. Sint Michielsgestel is also for the natural approach, encouraging residents to hang up nesting boxes by contributing five euros to each one.

Amsterdam is also planning on hanging up a huge number of bird boxes in the Amsterdam Forest (Amsterdamse Bos). Zaltbommel has provided the renovated city walls with breeding boxes for tits. In total, 38 municipalities are taking the natural predator approach. 

Using organic pesticides

Of the 200 municipalities that responded to the NOS survey, 60 are opting to use organic pest control. Neder-Betuwe, for example, has experimented with a bacterial preparation. Oak trees treated with this substance did not have any oak processionary caterpillars on them last summer. The municipality also tested the use of nematodes, sprayed onto the trees in two cycles. In this test, the caterpillars also disappeared. Neder-Betuwe wants to use both methods this coming year.

Sitard-Geelen and various other municipalities in Limburg have also reported success using bacterial preparations. The downside to this method, however, is that it doesn’t just target the oak processionary caterpillar, rather all types of caterpillars and butterflies.