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Mass outbreaks of Oak processionary moth (Thaumetopoea processionea L.), noticed since 1998, have increased dramatically this year. Whereas at the beginning of the gradation only single trees and smaller forest areas were infested now caterpillar nests and processions as well as heavy defoliation can be observed in numerous tree crowns in the eastern part of the Viennese Forest (Lainzer Tiergarten and surroundings), of the Hochleithen Forest near Wolkersdorf/Lower Austria, but also in alleys (Hermesstraße etc.) and gardens in the suburbs of Vienna. They feed especially on (Quercus cerris), but also sometimes on Carpinus betulus as well as on other oak species. Pest and damage symptoms The Caterpillars are reddish brown and hairy. They form real processions along the tree stems and feed especially on the leaves during the night, leaving behind only the leaf veins. In June, heavy, sometimes also total defoliation was observed. Noticeable are the 1,5-2 m large caterpillar nets which are fixed at the stem or at the nesting boxes for starlings in the tree crown by means of span threads. The yellow to red brown puppet cocoons in ton form are arranged close to each other, honeycombed in the caterpillar nest. The flight of the moth (reveller) begins normally mid of July. Danger from direct contact As the poisonous hairs (setae) contain an urticating toxin especially harmful to humans causing irritant dermatitis , it is very important to be careful. Neither caterpillars nor caterpillar nests should be touched. Even breathing in airborne setae may cause respiratory distress. In case of allergic symptoms a dermatologist should be seen immediately.