Which body part is referred to as the "waist" of the ant?

The "waist" of the ant is referred to as the petiole. This structure is significant because it connects the thorax to the gaster in ants, giving them a distinctive appearance. The petiole can be considered a narrow segment that determines how flexible an ant can be and allows movement between the body segments. In many ant species, the presence of a petiole marks a clear demarcation between the abdomen and the thorax, contributing to identification and classification.

Other body parts listed, such as the gaster, head, and thorax, serve different roles. The gaster primarily contains the digestive organs and reproductive structures, while the head houses vital sensory organs and mouthparts. The thorax is responsible for locomotion, containing the legs and, occasionally, wings. Thus, the petiole uniquely serves as the connecting "waist" that is essential for the characteristic structure and movement of ants.