Like human beings, insects exhibit varying degrees of sociality. One particular form of social organization that is uniquely found in insect species is known as eusociality. Eusocial species are characterized by a highly organized social structure that features a division of labor and cooperative care of young.
The term “eusociality” was first introduced into the scientific canon in 1966 by entomologist Suzanne Batra who used the term to describe the social organization and behavior of bees. In the early 1970s, biologist E.O Wilson adopted the term and extended its definition to include other social insects such as bees, termites, and wasps. According to the classical definition, eusocial insects include organisms that exhibit the following key characteristics:
- Reproductive division of labor
- Overlapping generations
- Cooperative care of young
A common feature of eusocial insects is the formation of specialized “castes” of insects that either possess or lack features/abilities found in individuals belonging to other castes.
Eusociality Case Study: Honey Bees
A commonly cited example of eusocial organisms is the honey bee. Honey bees display a regimented social hierarchy with specialized castes of insects dedicated to specific tasks. Biologists have identified three key castes of honey bees: workers, the queen, and drones. Worker bees are responsible for maintaining the hive, foraging for food, and caring for broods. Worker bees typically rotate through various duties throughout their life, beginning as nurses for the young and transitioning to foragers later in life.
The queen is the sole sexually developed female in the hive whose primary purpose is reproduction. Queen bees produce up to 3,000 eggs per day and produce the pheromones that act as the social “glue” holding the hive together. Drones serve one singular purpose, to fertilize the queen. Drones are the largest bees in the hive, have very short life spans, and usually die as soon as they mate with the queen.
The division of labor within honey bee hives is considered a paradigm example of eusocial organization. Each bee performs a specific task relevant to the survival of the group, and each individual bee relies on others performing their assigned tasks. Multiple generations of honey bees live together in the same hive and all contribute to the colony’s survival.
Eusociality in Other Insects
Other species of insects that demonstrate eusociality include ants, wasps, and termites. For example, ants, like bees, are divided into distinct castes that handle specific tasks in the colony, including the queen, soldier ants, worker ants, and drone ants for reproduction. In certain species of the paper wasp, dominant females handle the maintenance of the hive and laying eggs while subordinate females forage for food and take care of the young.
An extremely common general division found in eusocial species is a distinction between reproductive and non-reproductive castes. Although members of the same species, members of different castes can develop significant morphological differences relevant to their responsibilities in the colony. For example, some members of termite species develop overly large mandibles for defense from predators. These mandibles can get so large they cannot properly feed themselves and must be fed by worker termites.
Eusocial social organization can also manifest in extreme altruistic behavior among members of the colony. For instance, worker specimens of honey ant colonies will sometimes fill their body cavities with liquid food and hang themselves upside down to act as food storage for other insects. Altruistic and self-sacrificial behavior is a common feature seen in eusocial insects.
Naked mole rats are the only known species mammal considered to be eusocial though both meerkats and dwarf mongooses exhibit some eusocial characteristics.
Are Humans Eusocial?
E.O Wilson famously (or perhaps infamously) argued that human beings can be categorized as “eusocial apes,” but his arguments have been met with criticisms. Fitting with the definition of eusociality, humans do exhibit cooperative brood care, altruistic behavior, and cohabitation of multiple generations. However, unlike eusocial organisms, human beings do not have an obviously biologically determined caste system.
Moreover, some critics have cautioned against the negative social consequences that would arise from believing humans to be eusocial, such as the idea that individuals’ place and function in society are determined by their biology.