Hatches of Rocky Mountain locusts (Melanoplus spretus) in 1874 and 1875 brought swarms up to 1,800 miles long and 110 miles wide across the Great Plains. Numbers were estimated in the trillions. Farmers risked starvation. The swarm is believed to have been the largest mass of living insects ever witnessed by modern man—but within thirty years the species disappeared. “I can’t believe M. spretus is extinct,” said ecologist Dan Otte in 2014. “But where to look for it?”