Self-Propelling Picnic Pests

Lauren I. Rugani

Many animals use a fight or flight response when confronted by a predator. Luckily for Odontomachus bauri, more commonly known as the trap-jaw ant, a single biological mechanism can be used for either reaction. The insect’s distinctive rapid mandible strikes may be used for predatory purposes or as a form of defensive motion.

Researchers at the University of California, Berkeley, at California Academy of Sciences in San Francisco and at the University of Illinois at Urbana-Champaign have recorded the complete mechanics of mandible use via high-speed videography. As reported in the Aug. 22 issue of PNAS, they calculated the kinematics and forces of a mandible strike and analyzed the aerial trajectory of the ant when it used the mandibles for propulsion.

The team observed two distinct types of ballistic propulsion that resulted from mandible strikes. During the most frequently observed behavior, termed “bouncer defense,” the ant simultaneously strikes an intruder and propels itself away — in some cases also repelling the intruder. These jumps ranged an average of 22.3 cm horizontally and up to 5.7 cm vertically.

The ants also displayed “escape jumps,” where they avoided an intruder altogether by striking the substrate upon which it stood and projecting upward. These jumps carried the ant an average of only 3.1 cm horizontally, but reached heights of up to 8.3 cm and kept the ant airborne nearly twice as long as bouncer defense jumps.

In all mandible strikes, the appendages closed one after the other, with the second mandible reaching a faster speed than the first. With speeds ranging from 35.5 to 64.3 ms, the mandible strike is now the fastest known predatory movement. The mandibles decelerate before they cross, perhaps to avoid self-injury from the force of the strike, which can reach up to 500 times the creature’s body weight.