What Is Spruce Budworm?

The eastern spruce budworm (Choristoneura fumiferana) is a native insect that causes damage to balsam fir and spruce trees during the larval (caterpillar) stage. Under normal (endemic) conditions, spruce budworm (SBW) populations are so low that this insect can be hard to find in Maine. However, SBW is capable of widespread outbreaks (epidemic conditions) that can cause extensive damage and mortality to Maine’s spruce-fir forests after several years of feeding. During epidemic conditions, defoliation is heavy enough that affected trees produce very little wood and many thousands of trees die. In addition to reduced natural resources and diminished water quality, local employment for those who rely on Maine’s forest-based economy can also be impacted by a SBW outbreak.