Which flightless katydid forms large migrating bands in western North America?

The flightless katydid that forms large migrating bands in western North America is the Mormon cricket.

Despite its name, the Mormon cricket is not a true cricket. It is a shield-backed katydid, Anabrus simplex, in the family Tettigoniidae. Adults cannot fly, but during population explosions they move across rangelands in dense, advancing bands.

These bands can contain millions of insects and reach densities of about 100 individuals per square meter. A marching Mormon cricket may travel up to 2 kilometers in a day. Swarms can damage crops, strip vegetation, and make roads slick when crushed beneath vehicles.

Researchers have found that the migrations are driven partly by the search for protein and salt. Cannibalism also helps keep the insects moving: crickets approaching from behind may eat slower individuals, creating pressure to continue forward. The name recalls encounters between the insects and Mormon settlers in Utah.