Some insects are called social insects as they live together in groups called colonies.
The true social insects—all ants and termites, and some bees and wasps—comprise 75 percent of the world's insect biomass, according to E.O. Wilson. A colony of social bees can number in the tens of thousands, and hundreds of millions of ants can live together in a supercolony of interconnected nests.
So what makes social insects behave the way they do? There are several theories, as well as varying degrees of social behavior.
Advantages of Social Behavior in Insects
Why have some insects evolved to live in large, cooperative colonies? There's strength in numbers. Social insects gain several advantages over their solitary cousins. Social insects work together to find food and other resources and to communicate their findings to others in the community. They can mount a vigorous defense of their home and resources when under attack.
Social insects also can outcompete other insects, and even larger animals, for territory and food. They can quickly construct a shelter, and expand it as needed, and they can divide chores in a manner that ensures everything gets done expeditiously.
Characteristics of Social Insects
So how do we define social, when speaking of insects? Many insects exhibit social behaviors, such as aggregating in large numbers at times. Gregarious behavior does not, by itself, mean an insect is social.
Entomologists refer to true social insects as eusocial.
By definition, eusocial insects must exhibit all 3 of these characteristics:
overlapping generations
cooperative brood care
a sterile worker caste
To give an example, think of termites. All termites are eusocial insects. Within a single termite colony, you will find individuals at various stages of the termite life cycle.
Generations of termites overlap, and there is a constant supply of new adults prepared to assume responsibility for the colony's care. The community cares for its young cooperatively.
Termite communities are divided into three castes. The reproductive caste is comprised of a king and queen. The soldier caste of both males and females is specially adapted for defending the colony. Soldiers are larger than other termites and are sterile. Finally, the worker caste consists of immature males and females that do all chores: feeding, cleaning, construction, and brood care.
Solitary insects, by contrast, don't exhibit any of these social behaviors.