From 1/5 to >1/.5" long. Front pair of wings are leathery; immature stages lack wings. Color varies with species: yellow, green, to tan; hind legs well developed for jumping.

Grasshopper injury to corn consists primarily of leaf feeding. Heavy losses may occur from feeding on plant stems or ripening kernels of grain.

Throughout the latter half of the growing season, particularly following several dry years (statewide)

Count numbers of grasshoppers per square yard as you move through the field or field margin.

Within the field, 3 - 7, 8 - 14, 15 or more hoppers per square yard indicate light, moderate, or heavy populations, respectively. In field margins, 11 - 20, 21 - 40, and more than 40, respectively.

http://www.unl.edu/entomology/extension/crops/fieldcorn.shtml