Since its rediscovery in Reusel in 1987 Thaumetopoea processionea has become a serious problem at many localities in The Netherlands. In the last three years many oak trees in the southernmost provinces of Noord-Brabant and Limburg were completely defoliated by caterpillars. Urticating hairs of larvae of the species caused serious problems in man and animal. Information on biology and distribution is given.