What is Eusociality? The Hidden Social Hierarchy of Animals

Ants live in incredibly organized, socially complex colonies where the division of labor is clearly defined. Each ant has a job to do, and by working together, the colony can achieve what a single ant could never hope to realize. But ants are more than just social creatures; they are eusocial. Eusociality represents the highest level of social behavior.

What is Eusociality?

Eusociality occurs when insects or animals live in groups with strictly defined roles, in which one or more individuals reproduce while the others remain sterile and perform other tasks. The non-reproductive members work together to care for the young, who are not their own offspring but are likely to be their siblings. Eusocial animals usually have overlapping generations within the same colony or group.

When Was Eusociality First Observed?

Entomologist Suzanne Batra first coined the term “eusocial” in 1966 when she was studying the social behavior of sweat bees. Batra noticed that one queen bee would lay eggs while several generations of her young stayed with her, forming the colony. These bees did not mate or lay eggs; instead, they collected pollen, built the hive, and cared for the young.

Batra explained to American Scientist, “I later coined the term ‘hypersocial’ for honeybees: They’re so social that the queen is never on her own. A solitary bee has to do it all, start a nest by herself, and everything. I came up with eusocial to mean ‘truly social.”

What Species Are Eusocial?

The eusocial species we are the most familiar with are insects that have queens for reproduction. Many are in the phylum Arthropoda, such as ants, bees, termites, and wasps.

However, among mammals, naked mole-rats (and Damaraland mole-rats) are also eusocial. Naked mole-rats live in colonies that typically average around 60 to 75 individuals, but some colonies can have as many as 295 members, all living underground in complex burrows and tunnels. Like bees, these animals have one queen that breeds while the others do the work of caring for the colony.

There are also species of snapping shrimp that behave like bees in a colony, even though they live in the ocean. These fascinating little sea creatures live in colonies guarded by males. The males’ job is to protect the egg-laying queens. The non-egg-laying individuals feed the young until they are ready to join the adults at work.

How Does Eusocial Behavior Look?

Because only one or a few individuals are responsible for reproduction, workers in eusocial colonies can focus on specific tasks that benefit the entire group. As a result, the non-reproductive members are highly efficient, never needing to expend energy on reproduction.

What is the Key Factor in Determining Eusociality?

Humans and other animals that live in groups, such as wolves and lions, are not considered eusocial because they do not have a biologically determined caste system that separates workers from reproducers. People and plenty of other mammals live in groups, care for each other’s young, and live together for several generations. However, the key difference is the existence of specialized behavioral groups with a clear division of labor, and the fact that some members lose the ability to reproduce.