A grex, (also called a pseudoplasmodium, or slug) starts as a crowd of single-celled amoebae of the groups Acrasiomycota or Dictyosteliida; grex is the Latin word for flock. The cells flock together, forming a mass that behaves as an organised, slug-like unit. Before they get stimulated to crowd together to form a grex, the amoebae simply wander as independent cells grazing on bacteria and other suitable food items. They continue in that way of life as long as conditions are favourable. When the amoebae are stressed, typically by a shortage of food, they form a grex.