A member of the non-reproductive laboring caste in semi-social and eusocial species.

The existence of a worker caste presupposes the existence also of royal (reproductive) castes. In termites, the term is used in a more restricted sense to designate individuals in the family Termitidae that completely lack wings and have reduced pterothorax, eyes, and genital apparatus.

A newly eclosed adult worker ant: The exoskeleton of a callow worker is still relatively soft and lightly pigmented.

"Eclose" refers to the emergence of an adult insect from a pupal case or an insect larva from an egg.

A member of the subcaste of the largest workers; especially, in ants: With ants, the subcaste of major workers is usually specialized for defense, so that an adult belonging to it is often also referred to as a "soldier".

In polymorphic ant series involving three or more worker subcastes: A media worker is one individual ant belonging to the medium-sized subcaste, or subcastes.

A member of the smallest worker subcaste: Minor worker in ant colonies are sterile female ants, very small, and although they do the most work, they do rest in order to get back their energy.

A dwarf worker produced from either the first ant broods or later ant broods that have been subjected to starvation: Nanitic workers occur in both monomorphic and polymorplhic species.