Mesothorax

The mesothorax is the middle of the three segments of the thorax of hexapods, and bears the second pair of legs.

Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal), the mesosternum (ventral), and the mesopleuron (lateral) on each side.

The mesothorax is the segment that bears the forewings in all winged insects, though sometimes these may be reduced or modified, as in beetles (Coleoptera) or Dermaptera, in which they are sclerotized to form the elytra ("wing covers"), and the Strepsiptera, in which they are reduced to form halteres that attach to the mesonotum.

In some groups of insects, the mesonotum is hypertrophied, such as in Diptera, Hymenoptera, and Lepidoptera), in which the anterior portion of the mesonotum (called the mesoscutum, or simply "scutum") forms most of the dorsal surface of the thorax.

In these orders, there is also typically a small sclerite attached to the mesonotum that covers the wing base, called the tegula.