. Defoliation of some Norway spruce stands, caused by Cephalcia abietis, was first reported in Romania in the autumn of 2015. The outbreak has affected 58 ha in the Eastern Carpathians and 190 ha in the Southern Carpathians. The species was previously known only as a faunistic element in the country and very little information on its biology, ecology, detection, forecast and population control is available in the Romanian literature. This paper is a synthesis of information concerning the web-spinning spruce sawfly, whose aim is to fill the knowledge gap. C. abietis is a species with a vast distribution area, but repeated outbreaks were reported especially from Central Europe. In the outbreak areas, the most insects of a generation need 2-3 years to complete their development, so that an intense flight and a stronger defoliation take place every 2-3 years. Although mortality factors affecting the populations of C. abietis are very numerous, they fail to keep defoliator populations under control and outbreaks may extend for a long time. Mass multiplication occurs mainly in pure Norway spruce stands older than 60 years, at medium altitudes (600-1000 m), in places exposed to periodic drought or pollution. Biological and ecological peculiarities of this species make the prognosis of defoliation much more labor intensive than that for other defoliators, although quite uncertain. The chemical control, with partially selective insecticides (chitin synthesis inhibitors), was usual during recent decades, while biological control is still in the experimental phase. Consequently, greater emphasis should be placed on preventing mass multiplication of this species