Green Stink Bugs look vastly different when they are young. Green eggs are laid in clusters and look like small seeds. Once the group of eggs hatch, round larvae emerge and may be mistaken for beetles. Nymphs (juveniles) are mostly black with fine white lines crossing their backs. Red spots appear on the fringe surrounding the head and two orange-red spots mark the top of the elytra (wing covering). As they mature, more green coloration becomes apparent and they grow bigger with more angular elytra. By the time they are mature adults, they are completely green and their elytra is shaped almost like a shield with a triangular center.
Green Stink Bugs emit a foul odor when they feel threatened and are usually left alone because it smells quite acrid. The scent glands are located at the top of the green triangle on their 'backs' and the chemical disperses quickly. The smell is sometimes described as a mix of burning oil, hair and chemicals and may be sprayed, not secreted.