The Morton Arboretum reports the presence of oak slug sawflies on oak, and pear sawflies on serviceberry. Oak slug sawflies are most common on pin oak. Pear sawflies feed on hawthorn, serviceberry, pear, and other members of the rose family. Rose slugs are close relatives that feed on rose. Slug sawfly larvae appear as slimy, elongate, slug-like creatures. Oak slug sawfly larvae are yellow and green. Pear sawfly larvae are greenish black. Rose slug larvae are yellowish green.

They cause window-feeding on the host’s leaves. That is, they eat through one leaf surface or epidermis and eat the inside of the leaf, leaving one leaf surface intact. This remaining leaf surface is initially whitish but soon dries and turns brown. As the larvae mature, they lose their slimy coverings and appear more like the sawfly larvae that they are. They will be greenish with three obvious pairs of true legs and more than five pairs of prolegs. These older larvae will skeletonize the leaves, eating holes in the leaves and eating away the leaf margins.

Although slug sawflies are usually not numerous, it is important that correct control measures are used if the population is large enough to warrant treatment. Bacillus thuringiensis kurstaki or slug baits are not effective. However, many other chemical insecticides used for caterpillar or beetle control will provide control.