This is a Pinacate Beetle, also known as a Desert Stink Beetle or Clown Beetle. There are many different species around the world. They protect themselves by spraying a foul smelling fluid from their abdomen. Besides smelling bad, this liquid causes a burning sensation if it gets into a predator's mouth, nose or eyes. In the Sonora Desert, where this photo was taken, the Grasshopper Mouse has a special way of dealing with this defense. The mouse will grab the beetle and shove its back end into the dirt to block the spray. It then proceeds to eat the front half of the insect.