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

Ants of the ponerine genus Odontomachus employ a trap jaw mechanism fo r prey catching or defense. The mandible strike is released within les s than 10 ms upon stimulation of particular mechanosensory trigger hai rs. It is based on the storage of mechanical energy produced by the la rge but slow mandible closer muscle which cocks the mandible several s econds in advance of the strike. The strike is released from the catch by a small trigger muscle composed of tubular fibers. It features fas t potentials and highly synchronized activation of all its muscle fibe rs only a few milliseconds in advance of the strike. The trigger muscl e is supplied by two unusually large motor neurons that are enclosed i n a glial sheath. The trap jaw action is thus controlled by a system c omposed of 2 giant sensory and 2 giant motor neurons on either side. T he giant neurons are most likely monosynaptically coupled. The large a xon diameter and the synaptic coupling result in high conduction veloc ity 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.