In terms of social structure, which insects share a caste system?

Insects that share a caste system are characterized by a social structure in which individual members of the colony or community have designated roles. In the case of wasps and ants, both demonstrate a caste system where there are distinct roles: workers, soldiers, and reproductive individuals (usually queens). Workers are responsible for foraging, caring for the young, and maintaining the nest, while soldiers, if present, defend the colony. The queen's primary role is reproduction.

This structured organization enables these insects to efficiently divide labor, leading to improved survival and productivity within the colony. Wasps and ants exhibit complex social behaviors, including cooperation and communication, which reinforce their caste systems.

In contrast, termites do also have a caste system, but beetles do not typically demonstrate such social structures akin to those found in wasps and ants. Similarly, bees exhibit a caste system but butterflies typically do not form colonies with social structures. Flies and moths also lack the social hierarchy that is characteristic of the insects mentioned in the correct answer. Thus, wasps and ants are the clear representatives of insects with a pronounced caste system.