As with many forest pests, the spruce budworm damage is more visible than the insect itself. Budworm feeding typically starts at the tops of trees. Affected spruce and fir often look scorched from budworm feeding in late June through July because many partially chewed needles become discolored and get caught in budworm webbing. Up close, new shoots of spruce and fir will have many missing and partially chewed needles (Figure 1). After multiple years of feeding, trees will start to die and will have a brown and eventually gray appearance (Figure 2).
The full-grown caterpillars have a dark, shiny head and dark brown bodies with light-colored spots along their backs (Figure 3). They are found from May through June. Pupae may be found within webbing at the end of twigs. Adult moths are small (less than one-inch wingspan) and mostly grey but may be reddish-brown with dark markings (Figure 4). They may fly to lights in great numbers in late June or early July.
Figure 1: Caterpillar with accompanying feeding damage, webbing, frass and webbed needles in early June.
Figure 2: Balsam fir and spruce mortality from spruce budworm defoliation in mid-June.
Figure 3: Spruce budworm caterpillar in late June.
Figure 4: Spruce budworm moths and eggs on balsam fir. Photo by K.B. Jamieson, Canadian Forest Service, Bugwood.org.