The adult elm sawfly, is 3/4 to 1 inch long, dark blue, parallel-sided and females have four small yellow spots on each side of the abdomen. The full grown elm sawfly larva is 1-½ inches long, greenish-yellow with a black stripe down the center of the back. Conifer sawflies have somewhat more compact bodies and the antennae of females are feathery. Common sawflies are wasp-like, often brightly colored and up to 3/4 inch long. Larvae can change in appearance and coloration through developmental stages.
Life cycles vary by species, but generally they overwinter as a pre-pupa in a cocoon in the ground or other protected place, pupating in the spring. In early summer, adults lay eggs in or on plant tissue. Larvae develop through several stages (up to 6 instars) before pupating, producing one generation per year. Some species have several generations annually.
Adults are rarely seen and do not sting. They are called sawflies because females of most species have a saw-like structure on the tip of their abdomens used to inject eggs into plant tissue. Larvae feed of the leaves of plants and can occasionally become numerous enough to cause injury to some trees.
If it is determined that chemical control measures are needed, they should be directed toward the young larvae. Young larvae are much more susceptible to chemical applications than larger, more mature larvae. This is especially true when using biorational products such as insecticidal soap. If larvae are nearly full grown, control measures should not be attempted as chemicals will not be as effective, and most of the damage that the plant will sustain has already been done. Finally, because sawflies often feed in groups, chemical applications should be directed only to the areas they are feeding on; entire tree sprays are unnecessary unless populations are wide-spread throughout the plant.