The mighty mandibles of the trap-jaw ants are legendary in the animal kingdom. Members of the genus Odontomachus have specialized spring-loaded jaws that can snap shut at speeds of 60 meters per second, with forces that exceed 300 times their body weight. But in four species, those powerful jaws are not only great at catching prey, they can also aid in the ant's escape.
In a report published online in the journal PLOS One, Fredrick Larabee, a graduate student at the University of Illinois at Urbana-Champaign, and co-author Andrew Suarez, explored whether the ants' ability to escape predation using its powerful jaws actually increased its chance of survival. So they pitted the trap-jaw ant against a lethal predator, the antlion.
Antlions (Myrmeleontidae) are sit and wait predators. They don't pursue prey, they make the prey come to them; kind of like human hunters who hide out in tree stands above a feeder and blast away when the deer come to feed. Antlions create an indentation in the sand, then bury themselves beneath its base. Eventually, a victim stumbles into the pit, and as it struggles to climb out, the antlion simply reaches up and grabs hold. Dinner is served.
But the trap-jaw ant has a handy weapon at its disposal: its jaws. With a mighty snap, the trap-jaw ants can propel themselves out of the pit, thereby escaping from the awaiting grasp of the antlion. This suggests that the spring-loaded mandibles have been co-opted as an anti-predatory strategy in some trap-jaw species. The researchers wanted to test this theory.
Larabee and Suarez collected 228 trap-jaw ants and an equal number of antlions. To test the trap-jaws' rate of survival, they glued 1/3 of their jaws shut, which meant the ants could no longer rely on their jaws to propel them out of the antlion's trap. They allowed the antlions to construct their pits, then introduced the trap-jaws and sat back and watched.
"The [unglued] ants were able to jump out of the pits about 15 percent of the time in their encounters with antlions," Larabee says. "But when we glued their mandibles shut before dropping them in the pits, they couldn't jump at all. It cut their survival rate in half."
So what does this mean from an evolutionary standpoint? It serves as another example of "co-option," where a feature that evolves for one purpose is co-opted to serve another, thereby increasing an organism's chance for survival. The trap-jaw ants have co-opted their powerful mandibles for escape, harnessing their amazing strength to propel themselves out of danger.
Perhaps in a million years or so, the antlion will evolve a counter-strategy.
