Mandible movements in ants.

Ants use their mandibles for almost any task, including prey-catching, fighting, leaf-cutting, brood care and communication. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Fast contracting fibers have short sarcomeres (2-3 microm) and attach directly to the closer apodeme, that conveys the muscle power to the mandible joint. Slow but forceful contracting fibers have long sarcomeres (5-6 microm) and attach to the apodeme either directly or via thin thread-like filaments. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain why species that rely on fast mandible strikes, such as predatory ants, have elongated head capsules that accommodate long muscle fibers directly attached to the apodeme at small angles, whereas species that depend on forceful movements, like leaf-cutting ants, have broader heads and many filament-attached fibers. Trap-jaw ants feature highly specialized catapult mechanisms. Their mandible closing is known as one of the fastest movements in the animal kingdom. The relatively large number of motor neurons that control the mandible closer reflects the importance of this muscle for the behavior of ants as well as other insects.