JAWS THAT SNAP - CONTROL OF MANDIBLE MOVEMENTS IN THE ANT MYSTRIUM

Ants of the genus Mystroium employ a peculiar snap-jaw mechanism in wh ich the closed mandibles cross over to deliver a stunning blow to an a dversary within about 0.5 ms. The mandible snapping is preceded by ant ennation and antennal withdrawal. The strike is initiated by contact o f the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is store d by a catapult mechanism. Recording of closer muscle activity indicat es that the mandibles are not triggered by any fast muscle. Instead, w e suppose that activity differences between the left and right mandibl e muscles imbalance a pivot at the mandible tip and release the strike . The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and of a complex muscl e receptor organ shows that the mandibles are also adapted to function s other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks. (C) 1998 Elsevier Science Ltd. All rights reserved.