Mandibles of first-instar Heterocampa obliqua Packard bear distinct “cutting” teeth on their distal edges, whereas the mandibles of the second and later instars have smooth, nearly continuous cutting edges. These structural differences correlate with a change in feeding behavior as the larva switches from leaf skeletonizing in the first instar to blade-clipping its hosts, Quercus alba and Q. macrocarpa (Fagaceae), as the second through fifth instars. The mandible of Crinodes besckei (Hübner) retains distal cutting teeth throughout larval developement; but this species, which feeds on Gouania polygama (Rhamnaceae), does not exhibit any leaf skeletonizing behavior. The stipital lobe appears in the second instar of each species. It is hypothesized that this lobe buffers the maxillary palpus from the mechanical action of the mandible and aids the ingestion of leaf tissue in combination with movements of the mandibles, labrum, and hypopharynx.