The larval (caterpillar) stage of a small brown moth ( Choristoneura fumiferana). The spruce budworm overwinters as a young (second instar) larva in a silken shelter (a hibernaculum) and is active as temperatures become warm in spring. Outbreaks usually occur in mature forests of White ( Picea glauca) , Black ( Picea mariana), and Engelmann Spruce and Balsam Fir ( Abies balsamea), occasionally reaching epidemic proportions and creating wide areas of dead and dying trees. These, in turn, become potential fuel for wildfire.
Spruce Budworm is a group of closely related insects in the genus Choristoneura. They are serious pests of conifers, especially Western Spruce Budworm, Choristoneura occidentalis and its eastern counterpart Choristoneura fumiferana. There are nearly a dozen Choristoneura species, subspecies, or forms, with a complexity of variation among populations found throughout much of the United States and Canada.