Two-year research on societal impact and improved control of oak processionary caterpillar

Published on
May 29, 2020

A consortium of almost 20 organisations and municipalities will carry out research on the caterpillar in the coming two years. Main focus will be on the societal impact of the larvae of the oak processionary moth, combined with an improved monitoring system and control of the caterpillars. New insights should lead to an improved guideline on its control because, during the past few years, efforts to keep the caterpillar under control did not render the right results.

The oak processionary caterpillars are now reaching the phase in which they have itching hairs. The hairs cause among others itchy irritations on the skin and sometimes lead to serious health problems in people and pets. During the past few years, the nuisance caused by the oak processionary caterpillar has grown considerably in the Netherlands. This limits the accessibility and enjoyment of nature areas, for example for people who want to exercise or meet socially. Besides this, the oak processionary caterpillar gives rise to high management expenses. Biodiversity in general is coming under pressure by any biological substances used, that are also lethal for caterpillars of other butterfly-and moth species.

Despite the fact that the oak processionary caterpillar occurs in the Netherlands already for some 30 years, there are still many questions concerning the societal and ecological consequences of control measures. Not all is clear also yet on how to improve layout and management of the living environment to contain the impact.

Guidelines Control Oak Processionary Moth in the Netherlands

The fall of 2019 came with a high level of infestation and therefore the initial guidelines needed to be updated. The latest research will work out details on the effectiveness of the various control measures that the municipalities it concerns apply. For example, the chosen options for stimulating natural enemies by hanging up bird boxes or arranging flowery green strokes along roadsides. New knowledge is expected to improve the assistance to managers in the Netherlands, when they are looking for another landscape layout or checking the relationship of control of the oak processionary caterpillar with health risks and biodiversity.

Despite the fact that the oak processionary caterpillar occurs in the Netherlands already for some 30 years, there are still many questions concerning the societal and ecological consequences of control measures.

Societal impact: improved risk assessment

The Nivel (Netherlands Institute for Health Services Research) indicated last year that around June and July thousands of people had visited their general practitioner with skin complaints like itching, bumps and rashes. In Overijssel, North-Brabant and Utrecht 150 per 100,000 inhabitants, at a given moment, had seen their doctor about an itchy rash. The number of doctor's visits even went up to 275 per 100,000 inhabitants for children between 0 and 4 years. The new research will link, among others, the degree of health complaints with the abundance of the caterpillars. Besides this the health expenses will be depicted. This information can contribute to an improved risk-assessment and can also make measures more precise.


The basis of a proper containment of the caterpillars of the oak processionary moth is having insight into the development of the number of caterpillars and moths, but it's success is also depending of the containment measures itself. At the moment, a nationwide or regional overview of the situation is hard to reach, because of the different ways of local monitoring and storing of the observations. Existing monitoring protocols have to become aligned with each other, so data may be compared and interchanged.

Nearly twenty organisations and muncipalities

Wageningen University & Research will carry out the research in collaboration with Nivel and partners of the Kenniscentrum Eikenprocessierups (= Dutch knowledge centre for OPM). Coordination of the all-Dutch consortium will be done by the Vereniging Stadswerk Nederland, the other participating parties are Stichting De Groene Stad, the Vereniging van Bos- en Natuurterreineigenaren, eleven municipalities (Amersfoort, Bergeijk, Dalfsen, Ede, Emmen, Hardenberg, Raalte, Rijswijk, Scherpenzeel, Tilburg) and the municipal co-operation CGM (Cuijk, Grave, Mill) and ProRail. The research is co-funded by the Topsector Horiculture & Starting Materials.