Lygus hesperusadults are about a quarter-inch long and a tenth of an inch wide and are flattened on the back. They vary from pale green to yellowish brown with reddish brown to black markings, and have a distinct, but small, yellow or pale green triangle in the center of the back. This distinguishes them from other insects.
Nymphs are uniformly pale green with red-tipped antennae and look similar to aphids. They can be distinguished from aphids by their more rapid movements. Larger nymphs have five black spots on the upper body surface, two on the segment immediately behind the head, two on the next segment, and one in the middle of the abdomen. Nymphs do not have wings.
A similar non-pest species that may be confused with lygus, Calocoris, frequently is found when monitoring weed and legume crop hosts for lygus. Calocoris has two prominent black dots on the back, just behind the head, and dark wing tips. Lygus adults have no black dots on the back. Both nymphs and adults of Calocoris are longer and narrower than lygus.
Other insects may also be confused with lygus, including beneficials such as the big-eyed bug.