On July 14, 1931, Governor Warren Green of South Dakota makes an urgent plea to President Herbert Hoover for assistance for his state's farmers, whose lives and livelihoods were being threatened by a catastrophic insect invasion. "Grasshoppers have utterly destroyed all crops in 11,000 square miles of South Dakota," the governor wrote in his emergency declaration. "Unless Federal aid is given, there will be intense suffering."

The insects couldn't have come at a worse time—as the Great Depression was raging and a bad drought had descended on the nation's midwestern breadbasket. During July, a swarm of grasshoppers had descended on crops throughout the heartland, devastating millions of acres and decimating food stores for humans and animals alike. As Missouri's Springfield Press reported two weeks later, "Ravenous grasshoppers of a nonmigratory but exceptionally greedy variety swarmed in wriggling hordes Wednesday over more than 46,875 square miles of farm lands in five middle western states and caused damage of which crop experts could say only that 'it will run into the millions.'"

Since the very beginning of agriculture, people have struggled to prevent insects from eating their crops. Locusts and grasshoppers, insect cousins, are among the most feared pests. A plague of these insects can occur when conditions cause their populations to suddenly explode. Usually this happens under drought or very dry conditions, since their egg pods are vulnerable to fungus in wet soil. When the soil is very dry, swarms can develop.

Professor Jeff Lockwood of Wyoming describes being in a swarm as follows: "They explode from beneath your feet. There’s sort of a rolling wave that forms out it front of you. They hit up against your body and cling against your clothes. It’s almost like being immersed in a gigantic living being."

The July 1931 swarm was said to be so thick that it blocked out the sun and one could shovel the grasshoppers with a scoop. Cornstalks were eaten to the ground and fields left completely bare. Since the early 1930s, swarms have not been seen in the United States. However, North Africa and parts of the Middle East continue to experience problems with insect swarms, which sometimes includes as many as 1 billion bugs.