J is for June Beetle.

Adult June Beetles feed on the foliage of many shrubs and trees and occasionally attack fruit trees and berries. Colorado's mountains serve as a great feeding place for these beetles.
Adult June Beetles reach about one-inch in length and one-half an inch in width. One generation of adults matures each year. Larvae are burried over a foot into the soil and during the spring make their way to the surface feeding on decaying plant matter. They pupate in May and adults emerge in early July and August.