This is a shield-backed bug. They greatly resemble stink bugs. Most adults are 8- to 10-mm long and feed on plants. This individual is an immature, called a nymph.
Photograph: © 2010 RKD Peterson
Date of Photograph: 22 July 2010
Location: Montana, Gallatin Co. (45o43’41” N 111o08’11” W)