THE SENSORY BASIS FOR THE TRAP-JAW MECHANISM IN THE ANT ODONTOMACHUS-BAURI

Ants of the ponerine genus Odontomachus have evolved a mechanism that allows them to instantaneously close their long mandibles to catch pre y or defend themselves. This trap-jaw action is triggered by contact o f trigger hairs with a potential prey item. Two of these long mechanos ensory hair sensilla reside proximally on each mandible and are suppli ed by giant sensory cells. Extracellular recordings demonstrate that t he sensory cells respond to tactile stimulation. Their phasic response s encode amplitude and velocity of hair-deflection away from the midli ne, but not hair position. The discharge of action potentials follows stimulus frequencies of more than 300 Hz. During sinusoidal stimulatio n, the cells adapt very little, sustain discharge rates of more than 2 00 Hz for more than 20 s, and reach peak spike rates of about 450 Hz. The afferent axons of these sensory cells give rise to huge axon termi nals within the suboesophageal ganglion. One of the afferents has a pr ominent contralateral branch, the other is confined to ipsilateral neu ropil. Anatomical data indicate that the 4 afferents may be coupled an d may serve as the substrate for a very fast reflex.