Both species are grayish black bugs with red eyes and red markings and are about a half-inch long as adults. The boxelder bug has three red stripes behind the head, red lines on the outer edges of the wings, and a red margin on the back edge of the front half of the wings. The red-shouldered bug has only two red stripes behind the head and has no red on the wings. Young bugs (nymphs) are smaller and do not have fully developed wings. They usually have more red markings than adults.
Ray Ridlen is an agriculture/horticulture educator for the Oklahoma County Extension Service. His column addresses frequently asked horticulture questions. For more information, call 713-1125.