What is a key characteristic that distinguishes insects from other arthropods?

Insects are distinctly characterized by their body structure, which is organized into three main regions: the head, thorax, and abdomen. This tripartite body plan is a fundamental feature that sets insects apart from other arthropods, such as arachnids, which typically have two body segments (the cephalothorax and abdomen). Additionally, insects possess one pair of antennae, which are important sensory organs. This characteristic further emphasizes their uniqueness within the broader category of arthropods.

While some insects may have wings, it is not a mandatory feature for all insects, nor do all insects have fused head and thorax like certain other arthropods, nor do they possess four pairs of legs, as insects always have three pairs. Thus, the defining traits of three distinct body regions and a single pair of antennae are key to identifying and classifying insects correctly within the arthropod family.