What do all adult insects have in common?

The characteristic that all adult insects share is having three pairs of jointed legs and three distinct body regions: the head, thorax, and abdomen. This structural feature is fundamental to the classification of insects and is part of their overall body plan. The three pairs of jointed legs enable insects to move in various ways, adapt to their environments, and engage in activities such as building nests, hunting, or avoiding predators.

Insects also possess three body regions that serve specific functions, such as sensory perception, locomotion, and reproduction. This anatomical structure is what differentiates insects from other arthropods, which may have different leg arrangements or body segments.

While some insects have two pairs of wings and an exoskeleton made of chitin, not all adult insects possess wings, making this characteristic not universal among all insects. The ability to produce silk is limited to certain groups, such as caterpillars and some adult moths and spiders, which means it does not apply to all adult insects. Thus, the structure of having three pairs of jointed legs and three body regions is the most inclusive and defining trait of adult insects.