Pristiphora rufipes is an insect related to ants, wasps and bees (Hymenoptera) with a larval stage that looks like a caterpillar (larvae of Lepidoptera). The adult is a typical-looking sawfly— like a wasp with no waist— about ¼ inch long. It is mostly black with some whitish markings on the head and pale orange legs. The females lay eggs on the leaves in late spring, and the green larvae with dark heads begin feeding on the leaf edges. The larvae are only active in late spring, usually from April to June. If numerous, they can devour all the leaves, leaving only the stripped stems and flowers. Their feeding damage is primarily cosmetic and even columbines that are completely defoliated will recover. Unless stressed by other factors, within a few weeks it will put out another flush of leaves. The larvae eat inward, eventually consuming everything but the midvein as they grow up to about ½ inch long. When they mature after a few weeks, the larvae drop off the leaves to pupate in brown, oblong cocoons amid leaf litter.
These sawflies are small and the same color as the leaves, and often feed on the underside of the leaves during the day, so they are easy to miss until defoliation is severe. Plants should be inspected frequently in spring, especially where these insects have occurred in the past, so that they can be controlled as soon as possible to prevent extensive plant damage. They are easy to pick or knock off the plants into a container soapy water.
If physical removal isn’t practical, insecticidal soap (Sevin) will kill the small larvae (but the spray must cover them) without affecting other animals. Because birds eat or feed sawflies to their young, other types of pesticides with residual activity should be used only as a last resort for severe infestations. If most of the leaves are already gone, cut the plant down to the ground and destroy the remnants.