Meet the cottonwood leaf beetle, Chrysomela scripta. These charming little beetles are about 6mm long. They are red, orange or yellow with black spots/broken black lines on the elytra, and a reddish or yellow margin on the thorax. Both adults and larvae really love leaves, to the point of skeletonizing them, and are serious defoliators of cottonwood (of course), willow, aspen and alder, depending on the location. Cottonwood leaf beetles occur throughout the United States.
Larvae start out black, becoming lighter and browner as they age, with white scent glands appearing as spots along the sides of their body. They emit a repellent smell from these glands when disturbed. They feed in groups when they are young, becoming more solitary as they get older.