Trap-jaw Ants Use Mandibles Not Only to Attack, But to Escape

Entomology Today May 13, 2015 Leave a Comment

Photo by Alex Wild. www.alexanderwild.com

Some species of trap-jaw ants may use their spring-loaded mandibles to hurl themselves out of harm’s way when an ant-trapping predator stalks them, according to a study published in the journal PLOS ONE by Fredrick Larabee and Andrew Suarez from the University of Illinois. This dramatic maneuver doubles the ants’ survival when other escape methods fail, the researchers found.

The mandibles of the trap-jaw ant Odontomachus brunneus can whip shut at speeds over 40 meters per second, and are used for capturing prey, protection, and more routine tasks such as digging nests or tending to ant larvae. Previous studies have reported that trap-jaw ants sometimes jump with their jaws, “but it was unknown whether this behavior was meant to help them get away from a predator, and it wasn’t clear that it actually improved their odds of surviving an encounter with a predator,” said Larabee.

To see if, and how often, the ants used the jaw-jumping maneuver to escape from an actual predator, the authors dropped trap-jaw ants into antlion pits in the lab. Pit-building antlions catch prey by first digging conical holes in the sand and burying themselves at the bottom to wait for an ant. Then the antlion might also hurl sand at the ant, causing a tiny avalanche that destabilizes the ant, causing it to tumble to the bottom of the pit where the antlion grabs it with its mandibles.

“The ants were able to jump out of the pits about 15 percent of the time in their encounters with antlions,” Larabee said. “But when we glued their mandibles shut before dropping them in the pits, they couldn’t jump at all. It cut in half their survival rate. This study may show how a trait or capability that evolved for one purpose can be adapted for different uses. In this case, a tool that is very good for capturing fast or dangerous prey also is good for another function, which is escape.”