Eusocial

Eusociality is the highest level of social organization in some animal species, characterized by cooperative care of young, overlapping generations within a single colony, and a division of individuals into reproductive and non-reproductive castes. In eusocial colonies, workers or other nonreproductive individuals perform tasks such as foraging, nest defense, and brood care for the benefit of the colony, often at the cost of their own reproduction.

Although most well-known in insects, eusociality has evolved in several groups including ants, bees, and termites, as well as some crustaceans such as certain shrimp. In many ants, bees, and wasps, a queen or queens reproduce while workers are largely sterile. In termites, a similar division of labor exists but with different developmental biology, as termites are more closely related to cockroaches. In Hymenoptera, haplodiploidy can increase relatedness among sisters, which has been proposed to promote the evolution of altruistic helping, though eusociality also occurs in diploid lineages where haplodiploidy is not a factor.

Colonies often exhibit division of labor by age or morphology (age polyethism or caste differentiation). Reproduction is typically centralized, but some workers may lay eggs in certain conditions, and queen replacement can occur. The adaptive value of eusociality is debated, with explanations based on inclusive fitness, ecological pressures, and kin selection, as well as colony-level selection in structured populations.

Today, eusocial species are model systems for studying sociality, cooperation, and complex organization. They present diverse life histories and social structures, from highly organized termite nests to large ant colonies, and continue to illuminate questions about evolution of cooperation and complex societies.