Have you seen any oak processionary caterpillars? Please report them!

You may come across them in the spring and summer: oak processionary caterpillars. During the months of May, June, and July, you may find these hairy caterpillars on oak trees. These small caterpillars can cause significant problems. Their stinging hairs can cause itching, rashes, and irritation to the eyes and respiratory tract. That is why the municipality is closely monitoring the situation and taking action where necessary.

The oak processionary caterpillar has been present in the Netherlands for many years. The caterpillar is the larva of a moth that lays its eggs in the crowns of oak trees, where it overwinters. Between mid-April and early May, the caterpillars hatch from the eggs. Initially, they are found high up in the tree. After several molts, groups of caterpillars gather and form large nests on the trunks of oak trees. After the fourth molt, they develop stinging hairs that can cause an allergic reaction in humans and animals. The nests consist of a dense web of threads, stinging hairs, molted skins, and excrement. From their nests, the caterpillars go out in processions at night in search of food.

Preventing Nuisance

The oak processionary caterpillar is a natural part of the environment, but we want to minimize any inconvenience as much as possible. By carefully identifying where the risks are greatest and by staying vigilant together, we can ensure that everyone can enjoy the outdoors safely. The approach in public spaces isn’t the same everywhere. The difference comes down to one key question: how many people will be there?

Where there are people, the risk is greater

In areas with high foot traffic—such as residential neighborhoods, schools, playgrounds, and shopping districts—the likelihood of complaints is higher. Children play here, people walk by every day, and there’s always activity. That’s why the municipality is taking swift and proactive action against the oak processionary caterpillar in these areas.

What does the municipality do if a nest is found in such a busy area?

Then:

we actively keep residents informed;
we ask that you report any issues;
we will put up warning signs if necessary;
and we'll remove the nest as soon as possible.

Immediate action is also taken when health complaints are reported.

Quiet spots

Not every area is equally busy. In parks, along bike paths, or on the outskirts of residential neighborhoods, there is some activity, but it is less intense. Here, the municipality has opted for a targeted approach.

Then:

we provide information via the website;
we ask residents to report nests via the BuitenBeter app;
and we remove nests when necessary.

Nature reserves

In nature, we give them space but remain vigilant. In remote areas and places where few people go, the likelihood of disturbances is lower. There, it isn’t necessary to remove every nest immediately.

That doesn't mean we're doing nothing.

Then:

we record reports;
we assess the situation;
and we take action if a risk does arise.

The approach also depends on the season. In the spring and early summer (January through July), the caterpillars are active and form nests. This is the most critical time to take action. Later in the year (August through December), the nests are often old or abandoned. These usually pose less of a risk, but can still cause problems. That is why we continue to monitor reports even during this period.

Your report helps

Have you spotted a nest of oak processionary caterpillars? You can easily and quickly report it using the BuitenBeter app. We review every report. The presence of the oak processionary caterpillar requires a careful assessment of risks in public spaces. These risks are closely linked to how intensively a location is used by people. The more activity there is, the greater the chance of nuisance or incidents.

Your report helps us quickly identify where action is needed. This can make all the difference, especially in busy areas.