According to species and circumstances, details of the shape of the grex and how it may form will vary but typically the stressed amoebae first produce pheromones that stimulate the flock to vertically assemble in a column. When the column of aggregated cells becomes too high and narrow to stay upright, it topples and becomes a slug-shaped mass: the grex.
According to species and circumstances, the structure of the grex and its formation can vary but typically stressed amoebae initially produce pheromones that trigger the flock to vertically assemble in a column. When this column becomes too tall and narrow, it topples into a slug-like mass: the grex.