Sawflies have larvae that look somewhat like caterpillars but are not, they are related to wasps. One sawfly that is active in Delaware is the dogwood sawfly. The following is more information.
Wasp-like adults emerge sometime in May through July and oviposit eggs onto the underside of leaves. Dogwood sawflies are serious pests of Cornus species, but seem to prefer Cornus racemosa and Cornus sericea. Larvae are active 1041-1914 GDD or when Aesculus parviflora is in bloom. First instars are difficult to spot because they are transparent yellow, but later instars are covered with a white chalky powder. Larvae feed gregariously and skeletonize leaves as early instars, but eventually consume entire leaves except for tough mid-veins. The last molt changes the larvae to a yellowish colored insect with a shiny black head and spots. Mature larvae overwinter in decaying wood. Parasitoids will attack dogwood sawflies and cultural control consists of hand-picking larvae from leaves. Chemical control options include horticultural oil, insecticidal soap, spinosad, acephate, carbaryl, imidacloprid, or one of the pyrethroids such as cyfluthrin or deltamethrin.
Dogwood sawfly larvae feeding. Photo by Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org
Information from Brian Kunkel, Ornamental IPM Specialist, UD