The Rocky Mountain locust (Melanoplus spretus) is an extinct species of locust that ranged through the 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 locust species, with one famed sighting in 1875 estimated at 198,000 square miles (510,000 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 Guinness World Records.