To march or not to march: Quantifying patterns of collective movement across swarming and non-swarming Schistocerca species

Phenotypic plasticity, the ability of a single gene to yield different phenotypes, delineates distinct phases within locust populations. Termed locust 'phase polyphenism’, this phenomenon results in either a solitarious phase that is characterized, among others, by a sedentary lifestyle and repulsion towards conspecifics, or a gregarious phase, where individuals show a greater level of activity and a high relative congeners attraction. In response to a changing environment, solitarious locusts switch to the gregarious phase, forming gigantic swarms of thousands marching juveniles and flying adults, devastating crops and impeding rural livelihood. This study aims to analyze the patterns of collective movement across swarming locusts, Schistocerca gregaria (the Desert Locust), and non-swarming grasshopper, Schistocerca americana (the American Bird Grasshopper), by tracking collective movement in an enclosed circular arena. Seven different densities were recorded for 6 hours and analyzed with an automated tracking software. Against our predictions, preliminary results showed no difference between S. americana and S. gregaria in the alignment, a proxy for directed coordinated motion. However, differences were found in the percentage of moving locusts and in the mean speed of moving individuals. While more analyses remain to be done, these results reframe the story and implications of S. americana being a species that was thought to lack swarming characteristics.