Anisotropic interaction and motion states of locusts in a hopper band

Swarming locusts present a quintessential example of animal collective
motion. Juvenile locusts march and hop across the ground in coordinated
groups called hopper bands. Composed of up to millions of insects, hopper
bands exhibit coordinated motion and various collective structures. These
groups are well-documented in the field, but the individual insects
themselves are typically studied in much smaller groups in laboratory
experiments. We present the first trajectory data that detail the movement
of individual locusts within a hopper band in a natural setting. Using
automated video tracking, we derive our data from footage of four distinct
hopper bands of the Australian plague locust, Chortoicetes terminifera. We
reconstruct nearly twenty-thousand individual trajectories composed of
over 3.3 million locust positions. We classify these data into three
motion states: stationary, walking, and hopping. Distributions of relative
neighbor positions reveal anisotropies that depend on motion state.
Stationary locusts have high-density areas distributed around them
apparently at random. Walking locusts have a low-density area in front of
them. Hopping locusts have low-density areas in front and behind them. Our
results suggest novel interactions, namely that locusts change their
motion to avoid colliding with neighbors in front of them.