Saddled prominent - maple, beech, etc. Uglynest caterpillar - cherry, etc. Walnut caterpillar - pecan, walnut, etc. Yellownecked caterpillar - hickory, oak Sawflies in the larval stage look very much like moth caterpillars. They may cause severe defoliation.
Sawflies belong in the group of insects which includes ants, bees, and wasps.
The single attack of a leaf-feeding insect will seldom kill a healthy tree or shrub. Repeated defoliations, however, may weaken and make them susceptible to destruction by other insects, diseases, severe cold weather, drought, etc. Most of those listed above are not a serious threat. Try to identify the specific insect before taking control measures. Your local Cooperative Extension Office can help.