What Does “A Cast of Crabs” Mean?
“Cast” is the most widely used collective noun for a group of crabs, and it borrows its imagery from the stage rather than the shore. A theatrical cast is a company of performers assembled together, and a cluster of crabs sideways-scuttling across a beach or tide pool has enough of that chaotic, milling-around energy to make the comparison stick.
There’s no strong evidence this is an old or formally documented term the way many hunting-derived collective nouns are. It reads more like a playful, borrowed word that got attached to crabs because the image fit, not because of any recorded species-specific history. Biologically speaking, most crabs are solitary and territorial rather than social, so “cast” is more of a whimsical label than a description of real group behavior, though some species, like Christmas Island’s red crabs, really do gather by the millions during their annual migration to the sea.
Example: “A cast of crabs scattered under the rocks as the tide pulled back.”
Related: Collective Nouns for Crustaceans · What Is a Group of Crabs Called?