Concept:Social insects survive through organised group living, especially the division of labour known as the caste system.
Explanation:Social insects such as ants, bees, wasps, and termites live in large colonies.
Within a colony, individuals are grouped into specialised castes: queens, workers, soldiers, and drones.
Each caste performs a distinct role: the queen reproduces, workers forage and build, soldiers defend the nest, and drones mate.
This division of labour makes the colony highly efficient and increases its chances of survival.
Migration and hibernation are seasonal avoidance strategies, not special social-insect adaptations.
Venom production is a defensive adaptation found in many organisms, but it is not the central adaptation that defines social insect survival.
Therefore, the formation of complex caste systems is the clearest example of an adaptation for survival in social insects.
Answer:C. Formation of complex caste systems