These acrobatic insects that are consuming the leaves of my Harry Lauder’s Walking Stick might resemble caterpillars but they are not. These are sawfly larvae, the larvae of not a fly at all but one of 4,000 varieties of a primitive stingless wasp. Look closely. The larvae of moths and butterflies have 1 to 4 sets of abdominal prolegs (false legs), whereas sawfly larvae have 6 sets of prolegs.
Mouthparts are for chewing and in great numbers they can defoliate a tree or shrub or flower. Most of them are somewhat host-specific and feed on foliage of specific trees and flowers. Some larvae work together on the leaf edges like these, some skeletonize leaves, some eat holes in leaves, some roll leaves, and some varieties create galls. The most common varieties here feed together and some hold their abdomen in the air like these. A defensive mechanism in many larvae is a row of glands on the abdomen that can expel an irritating fluid.
The benign winged sawfly adults are small and generally dark in color. They do not have the constricted waist of many stinging wasps and the females have a saw-toothed ovipositor, which is used to ‘saw’ into plant material and deposit eggs. There is only one generation per year but the larvae can be destructive if they are numerous enough. Ten years ago we were inundated with the Loblolly Pine Sawfly that destroyed a number of our young trees.
Ann Hohenberger, The Garden Club of Gloucester