Adult Thorn Bugs are half-inch long insects that are “true bugs” (members of the Family Hemiptera). As with other members of this family, Thorn Bugs have sucking mouthparts that allow them to pierce plant tissues and drink plant sap. As a result, Thorn Bugs can cause the death of some twigs and potentially introduce diseases to the plant. In most cases, Thorn Bug populations are very low and damage caused by plant bugs is minimal. The bugs are fascinating to watch and harmless to humans – unless you are barefoot and happen to step on an adult Thorn Bug.