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- top: A giant moray eel being cleaned by a cleaner fish and a burying beetle begins to prepare a carcass
- bottom: An adult olive baboon allogrooming and a doctor performing surgery
Social immunity is any antiparasite defence mounted for the benefit of individuals other than the actor. For parasites, the frequent contact, high population density and low genetic variability makes social groups of organisms a promising target for infection: this has driven the evolution of collective and cooperative anti-parasite mechanisms that both prevent the establishment of and reduce the damage of diseases among group members. Social immune mechanisms range from the prophylactic, such as burying beetles smearing their carcasses with antimicrobials or termites fumigating their nests with naphthalene, to the active defenses seen in the imprisoning of parasitic beetles by honeybees or by the miniature 'hitchhiking' leafcutter ants which travel on larger worker's leaves to fight off parasitoid flies. Whilst many specific social immune mechanisms had been studied in relative isolation (e.g. the "collective medication" of wood ants), it was not until Sylvia Cremer et al.'s 2007 paper "Social Immunity" that the topic was seriously considered. Empirical and theoretical work in social immunity continues to reveal not only new mechanisms of protection but also implications for understanding of the evolution of group living and polyandry.
Social immunity (also termed collective immunity) describes the additional level of disease protection arising in social groups from collective disease defences, performed either jointly or towards one another. These collective defences complement the individual immunity of all group members and constitute an extra layer of protection at the group level, combining behavioural, physiological and organisational adaptations. These defences can be employed either prophylactically or on demand.