Prothorax

The prothorax is the anterior-most of the three segments in the thorax of an insect. It is located immediately behind the head and articulates with the mesothorax.

The primary function of the prothorax is locomotion and support of the head. In most insect orders, the prothorax bears a pair of legs, and in some orders, such as Mantodea and Coleoptera, it is greatly enlarged and modified for specific functions, such as grasping prey or providing protection.

The dorsal portion of the prothorax is called the pronotum. The pronotum varies widely in size and shape across different insect groups and is an important diagnostic character in insect identification. In some insects, the pronotum may extend backwards to cover part or all of the mesothorax and metathorax. The ventral part of the prothorax is called the prosternum. The sides are called the propleura.

Unlike the mesothorax and metathorax, the prothorax typically does not bear wings in adult insects. A notable exception is the order Strepsiptera, where the males have modified halteres (balancing organs) on the prothorax. Because it lacks wings in most insect orders, the prothorax is generally more heavily sclerotized (hardened) than the other thoracic segments, providing structural support.

Muscles within the prothorax control the movement of the head and the prothoracic legs. Sensory organs, such as spiracles (respiratory openings), may also be located on the prothorax.