The Panel also considered the risk posed by this pest to the whole of the European Union. Based on a review of the scientific literature and consultation with European experts, the Panel concluded that the oak processionary moth may be considered eligible for addition to the EU list of harmful organisms, although a high level of uncertainty regarding the extent of plant health effects was noted.

The oak processionary moth lays eggs on branches of oak trees and its larvae live in groups and form a nest from which they migrate in procession to feed in the canopy of the trees. In addition to their effects on plant health, the caterpillars produce hairs which may cause allergic reactions in humans and animals.

The Panel considered that in the absence of natural barriers the insect may spread by natural dispersal, such as flight, to adjacent areas, and that it could be introduced to new areas by infested oak plants used for planting. Therefore, phytosanitary measures applied to those plants, such as pest surveillance, could reduce the probability of their infesting new areas.

Although currently present in many parts of Europe, the oak processionary moth has not been reported as established in Denmark, Estonia, Finland, Ireland, Latvia, Lithuania, Sweden, or Malta. Factors which limit the establishment of the insect, include the availability of oak and low summer temperatures. A preliminary climate analysis conducted by the Panel showed that the pest could become established also in southern parts of the most northern Member States.

A member of the PLH Panel expressed a minority opinion with regard to the consideration of the pest as a harmful organism.