Rapid-fire jaws propel ants to safety

Scientists using a high-speed imaging system have found that the jaws in trap-jaw ants snap shut in less than a millisecond, averaging a speed of 38 meters per second (approximately 137 kilometers/hour).

“Not only are these mandibles phenomenally fast, they also generate enough force to eject enemies and propel the ants through the air,” said Andrew V. Suarez, a professor of entomology and of animal biology at the University of Illinois at Urbana-Champaign, and co-author of a paper that will be posted online this week ahead of regular publication by the Proceedings of the National Academy of Sciences.

Trap-jaw ants (Odontomachus bauri) are found throughout Central and South America. The ants in this study were collected in Costa Rica. Typical prey includes termites and other ant species; predators include spiders, frogs and lizards.

“There is nothing obvious about the ants' prey that points toward the need for an extremely fast capture mechanism,” said Suarez, who is also an affiliate of the Institute for Genomic Biology at the U. of I. “Increasing speed generates more force, however, which can inflict more damage to predators or propel the ants to safety.”

Powered by a large head filled with muscle, the mandibles function like spring-loaded lever arms. An internal damping mechanism prevents the jaws from crushing each other.

Depending upon how the ants used their jaws, they produced power for predation or for two types of defensive propulsion, the researchers report.

The first type, termed bouncer defense, involved ants striking a large intruding object, simultaneously attacking the intruder while bouncing away, up to 40 centimeters in some cases, and sometimes causing the intruder to bounce away as well.

The second type of defensive propulsion was the escape jump. When a threat was too large, the ant would snap its jaws off the ground, launching itself up to 8 centimeters in the air.

Though not as high vertically, the horizontal ranges of the bouncer defense jumps averaged seven times greater than escape jumps.

“These propulsive behaviors may be especially important given that O. bauri builds nests in leaf litter, rather than below ground,” the researchers write. “Without the subterranean strongholds typical of many ants, temporary escape from predators and ejection of intruders may be essential for this species.”

To study the ants' movements, the researchers used a high-speed imaging system capable of taking up to 250,000 frames per second. Because the mandibles close so quickly, a complete analysis of jaw movement had not been performed before.