The oak processionary moth: a new health hazard?

British Journal of General Practice, August 2015 435 InTroduCTIon Although a native of southern Europe, the thermophilic oak processionary moth (OPM, Thaumetopoea processionea) is expanding its prevalence to encompass Central and Northern Europe. Roughly, over the past decade, the moth’s range has spread northwards and the species has now became established in the warmer regions of Northern France, the Netherlands, the UK, and Germany.1–3 In the UK, the moth occurs in Surrey and in parts of west London.4 It is thought that the northward progression is due to a decline in late spring frosts, resulting in a more synchronous egg hatch.4 Occurrence of caterpillar dermatitis has increased considerably, not only in gardeners, but also in people engaging in outdoor activities. The larvae of these caterpillars are equipped with fine, barbed hairs (setae, 0.2 mm), which can readily penetrate the human skin.5,6 One of the major issues with the hairs is that they readily detach and can then be blown via wind currents for considerable distances. The older larvae (fifth and sixth instars) are of particular concern as they can carry up to half a million of the urticating setae per caterpillar. The spines can be active for up to 10 years, posing a long-term threat to human health (Box 1). The caterpillars start emerging in late April, and can be seen marching on oaks in long head-to-tail lines in order to feed on the foliage of oak trees; hence the name ‘processionary’. They are the larval stages of the OPM and June is the time of the year when they build their distinctive silken, weblike nests on the trunks of oak trees, typically about the size of a tennis ball (Figure 1). Not only do the caterpillars contain numerous urticating hairs with microscopic barbs but so do the nests. Control of the OPM is warranted for health reasons if affected trees are located in the vicinity of preschools, schools, or recreational facilities. The highrisk period stretches from mid-May to the end of August.