THE FAST MANDIBLE STRIKE IN THE TRAP-JAW ANT ODONTOMACHUS .2. MOTOR CONTROL

Ants of the ponerine genus Odontomachus employ a trap jaw mechanism for prey catching or defense. The mandible strike is released within less than 10 ms upon stimulation of particular mechanosensory trigger hairs. It is based on the storage of mechanical energy produced by the large but slow mandible closer muscle which cocks the mandible several seconds in advance of the strike. The strike is released from the catch by a small trigger muscle composed of tubular fibers. It features fast potentials and highly synchronized activation of all its muscle fibers only a few milliseconds in advance of the strike. The trigger muscle is supplied by two unusually large motor neurons that are enclosed in a glial sheath. The trap jaw action is thus controlled by a system composed of 2 giant sensory and 2 giant motor neurons on either side. The giant neurons are most likely monosynaptically coupled. The large axon diameter and the synaptic coupling result in high conduction velocity which underlies the very fast mandible reflex. The reflex activity is modulated by antennal and other sensory input probably converging onto the large dendritic trees of the trigger motor neurons.