Most eusocial mammal

The most eusocial species of mammal, exhibiting a eusocial system much more advanced, extensive and specialized than in any other mammal, is the naked mole-rat Heterocephalus glaber, a burrowing rodent native to the dry savannah of Kenya, Somalia and Ethiopia, and the only member of an entire taxonomic family, Heterocephalidae. Eusocial mammals are ones that live in a caste system similar in operation to those famously exhibited by social insects, such as ants, various bee and wasp species, and termites. The naked mole-rat lives in subterranean colonies inside each of which labour is divided between different castes, as first documented in May 1981. The highest caste is the queen, which is the only breeding female in the colony (and also its largest specimen), mating with one or two select male consorts. All other members of the colony are sterile male and female non-breeders, and, depending upon their body size, serve either as workers (smaller male and female individuals, digging tunnels, foraging, bringing food and bedding materials to the communal nest) or as non-workers (larger male and female individuals, attending to the needs of the queen and her consorts, caring for her offspring, protecting the nest against potential attackers, repairing damaged tunnels). Non-workers dominate workers, and owing to the extensive inbreeding that occurs within a colony, its members are all virtually identical genetically to one another.

As its name reveals, the naked mole-rat is indeed virtually bereft of fur, and also lacks an insulating layer in its skin, both characteristics helping to prevent it from over-heating in the extremely hot, harsh terrain where it lives. Living underground, it also has very poor eyesight, but extremely powerful jaws and teeth that it uses for digging purposes.

When a colony's queen dies, a previously sterile non-breeding female in that same colony replaces her and becomes sexually active, serving from then on as the new queen.

According to research by Hudson Kern Reeve and colleagues at Cornell University in New York, USA, and Christopher Faulkes and colleagues at London's Institute of Zoology in the UK, this extensive eusocial organization can lead to a colony's members being so similar to one another genetically that it is as if they had inbred for 60 generations.