Rocky Mountain Locust

The Rocky Mountain locust (Melanoplus spretus) was the locust species that ranged through almost the entire western half of the United States (and some western portions of Canada) until the end of the 19th century. Sightings often placed their swarms in numbers far larger than any other species of locust, with one famed sighting having been estimated at 198,000 square miles (513,000 km²) in size (greater than the area of California), weighing 27.5 million tons, and consisting of some 12.5 trillion insects - the greatest concentration of animals ever speculatively guessed, according to The Guinness Book of Records.

But less than 30 years later, the species was apparently extinct, with the last recorded sighting of a live specimen in 1902 in southern Canada. And because no one expected such a ubiquitous creature to become extinct, very few samples were ever collected (though a few preserved remains have been found in Grasshopper Glacier, Montana). Though grasshoppers still cause significant crop damage today, their populations do not even approach the densities of true locusts. Had the Rocky Mountain locust continued to survive, North American agriculture would likely have had to adapt to its presence (North America is the only continent without a major locust species outside of Antarctica).