What Is Spruce Budworm?
The eastern spruce budworm (Choristoneura fumiferana) is a native insect that causes major damage to Maine’s spruce-fir forests on a regular cycle. Spruce budworm caterpillars feed on the buds and needles of fir and spruces. Under normal (endemic) conditions populations of this insect are so low that spruce budworm is hard to find. Periodically the budworm undergoes a population outbreak (epidemic) and becomes so abundant that serious feeding damage occurs. During epidemics 
defoliation is heavy enough that affected trees produce very little wood and many thousands of trees die.
- A native moth
- Undergoes complete metamorphosis
- Adult = moth
- Immature = caterpillar (causes damage)
- Caterpillar eats needles of fir and spruce trees (hosts), eating some within the bud before the needles expand (budworm)
- Spruce budworm is always present in Maine’s spruce-fir forests
- Usually hard to find
- Every 30-60 years populations outbreak, building to epidemic-levels in sync with maturing hosts
- Epidemic-level populations persist for many years