eusozial

Eusociality is the highest level of social organization observed in some animal species. It is defined by three core features: cooperative care of offspring outside the immediate family, reproductive division of labor in which usually only a subset of individuals reproduce while others work to support the colony, and overlapping generations within a colony that include both mature breeders and non-reproductive helpers.

The best-known eusocial groups are insects, especially ants, bees, wasps, and termites. In these taxa, colonies can consist of thousands to millions of individuals arranged into castes such as workers, soldiers, and queens. Eusociality also occurs in a few crustaceans and, more rarely, in vertebrates, with the naked mole-rat often cited as an example among mammals. Outside these groups, eusociality is comparatively rare, and its exact distribution across the animal kingdom remains a focus of research.

Evolutionary explanations for eusociality emphasize the combination of kin selection, ecological constraints, and social remodeling that supports cooperative breeding and division of labor. In many Hymenoptera, relatedness among colony members may be high due to haplodiploidy, potentially favoring altruistic helping towards relatives, though eusociality also exists in lineages without this genetic system. Ecological factors such as nest availability, resource distribution, and predation pressure can favor the maintenance of a nested, cooperative society. The study of eusociality informs broader theories of social evolution, inclusive fitness, and the emergence of complex society in nature.