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The larvae of the brown spruce longhorn beetle kill trees by tunneling into the cambium and phloem layers disrupting the essential transfer of nutrients. Heavy beetle infestations can girdle a tree cutting off the nutrient flow completely. A girdled tree invariably dies. Aside from members of the spruce family, in Europe, the beetles have been known to attack firs, pines, larches and, occasionally hardwoods.

There are aspects to the lifecycle of the brown spruce longhorn beetle in the Halifax outbreak which are still not well understood. Female beetles lay their eggs on the bark of host trees. Between ten and fourteen days later, the hatched larvae burrow into the tree tunneling through the cambium layer. At maturity (approximately two months), the larvae reach a maximum of one inch (2.5 cm). Prior to pupation, the larvae then tunnel into the phloem where pupation occurs. The pupation stage lasts approximately two weeks after which the adult beetle chews an exit hole in the bark. It has still not been determined whether there are one or two generations of the beetle per season. It is believed that the beetle larvae overwinter within the tree.

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