Structure and Mechanics of the Dragonfly Pterothorax1

The exact structure and movement of parts in the dragonfly flight mechanism are described and illustrated. The tergum, which articulates only with the wings, has 6 functional connections with each wing. Each wing has 2 fulcra. Wing twist is caused by a difference in elevation of the 2 wing base plates. Small, differently colored flight muscles appear to function tonically because of their length and positions. Phasic (rapidly contracting) muscles cancel their individual wing twisting forces when functioning together. Wing twisting is probably caused by relaxation of individual muscles. Phasic muscles are probably not able to produce delicate graded responses. As a result, small tonic muscles appear to function in gliding, adjusting wings of a dragonfly when at rest for balance in turbulent air, and damping to reduce power of phasic muscles of 1 side during turning.