When they are done feeding the larvae drop to the ground underneath the tree, where they burrow into the duff and pupate. Spruce Sawfly has the potential to defoliate a single tree in one season, however most of the time it only partially does so. Several consecutive seasons of repeated defoliation can kill a tree. Control the best time to control this serious insect pest is when the larvae hatch and just start to feed on the needles. For maximum efficiency the homeowner should examine the ornamental spruce for eggs or the small Sawfly larvae.
Caterpillar larvae have between two- five prolegs.
The body has lengthwise stripes. When scouting a tree for sawflies look for partially eaten needles hanging down from the twigs. If it's early spring, look for eggs in long rows on the needles. There are several insecticides that are very effective for controlling spruce sawfly.