Schistocerca americana is closely related to S. gregaria the desert locust of the Old World. Under the right ecological conditions nymphs of the locust are forced into high densities. The close contact of individuals triggers the release of seritonin which causes extensive morphological, behavioral, and physiological changes in the nymphs, causing them to become locusts. Phase polyphenism occurs in multiple subfamilies and some species exhibit some of the changes even if they do not swarm and become locusts. The individual on the left is a solitary cryptically colored individual from a cotton field. The grasshopper on the right is a gregarious aposematically colored individual reared in a lab colony at high density. Studies have shown that S. americana does not become gregarious and swarm yet as you can see it exhibits morphological phase polyphenism.