A caterpillar that poses a health hazard has arrived in the northern province of Groningen, having spread from southern Europe and through the rest of the Netherlands.

The caterpillar is laid by the Oak Processionary moth (thaumetopoea processionea) and sheds poisonous hairs which may cause skin irritation and breathing problems. It crawls in procession over the bark of oak trees forming a moving carpet of hairs.
With no known pesticide to kill them, pest controllers have been removing their nests from affected trees. It has now been discovered that the caterpillars also nest underground.