Scientists have shown that body-flinging escape jumps by trap-jaw ants are more than just a neat insectoid party trick.
As its name implies, the trap-jaw ant has an incredibly powerful chomp. As they bite down, their mandibles travel at an astonishing rate of 130 feet per second (40 m/s), with a total elapsed time of 0.13 milliseconds. The force of these bites is used by the trap-jaws to stun and disable their prey, like small insects, or rival ants.
But these mandibles do more than just provide offensive capabilities. As a team from UC Berkeley observed back in 2006, the intense force exerted by these bites is enough to launch the ant’s body through the air — an apparent defensive maneuver known as an “escape jump.”
To accomplish this feat, the ants contract the muscles in their head that are attached to the elongated mandible. Then they lock the spring-loaded mandibles in an open position with a latch.
(Photo credit: Adrian Smith)
“This allows the head to store and release a large amount of elastic strain energy in the cuticle of the head in addition to the energy stored directly in the muscle fibers,” explained entomologist Andrew Suarez to io9. “When the latch is released, the mandibles shoot forward incredibly quickly generating forces that can be a few hundred times the mass of the ant.”
(Larabee & Suarez, PLOS ONE)
Suarez, who works out of the University of Illinois at Urbana-Champaign, says that the mandibles, when they strike a hard surface like the ground, produce enough reflective force back onto the ant to send it flying through the air.
Dramatic, to be sure. But Suarez, along with graduate student Fredrick Larabee, wasn’t entirely sure if these jumps actually aided in the ants’ survival. To find out, they performed a series of experiments, the results of which can now be found at the open access science journal PLOS ONE.
Ants in the Sarlacc Pit
Larabee and Suarez sought to determine whether these leaps are a benefit to one particular species of trap-jaws, Odontomachus brunneus, when its members are confronted by a predatorial antlion, a winged insect of the Myrmeleontidae family.
A fateful encounter between a trap-jaw and antlion.
Like the fictional sarlacc in the pit, antlions wait at the bottom of their carved-out holes for unsuspecting prey. When a trap-jaw falls in, the lack of traction makes it difficult for the ant to get out. Making matters worse, the antlion loosens and kicks sand at its prospective meal, further destabilizing the surface. Once the ant falls within reach of the antlion, it’s game over.
Unless, of course, the trap-jaw ant successfully employs its proprietary escape maneuver.
During their experiments, Suarez and Larabee conducted 117 trials, each consisting of a single encounter between an individual trap-jaw and an antlion. The researchers incentivized the antlions by starving them for 48 hours.
A successful escape attempt via jumping.
When the trap-jaws fell into the pit, they were captured one-third of the time. But in 15% of the trials, the anti-jaws escaped by jumping with their mandibles. The remaining ants (~50%) were able to escape the pits by simply crawling out. Escape jumps always occurred after an antlion attack, and only 26.5% of jaw strikes produced jumps. In some cases, the antlions released a captured ant following a jaw strike, allowing the ant to escape the pit by running.
In a second set of experiments, the researchers glued the mandibles shut to test whether the jumps were improving individual survival. As the authors report in their study:
Restraining the mandibles of trap-jaw ants significantly decreased their ability to escape from antlion pits. Ants in the mock treatment and unrestrained control were 2.3 and 4.7 times, respectively, more likely to escape than the restraint treatment. Experimental manipulation (chilling and applying glue) reduced the escape success of individuals in the mock and restraint treatment by decreasing their ability to run out of pits. However, manipulation did not affect escape jump frequency of the mock treatment, and the increased survival of ants in this treatment compared with the experimental restraint treatment was due to their use of mandible strikes for jumping.
Gluing the mandibles shut essentially cut the ants’ survival rates down by half.
An Evolutionary By-product?
The researchers say this dual-capability is a good example of what biologists call “evolutionary co-option.” The mandibles, while performing offensive duties in one context, are doubling as a defensive mechanism in other.
It’s important to point out that the ants may not be snapping their jaws shut in a deliberate attempt to execute the escape jump.
“There is no doubt that the jumping behavior is a by-product of the force produced and in most results from a side-effect of the ant panicking or trying to bite the lion,” Suarez told io9. “However, in many cases it appears the ant is striking the side of the pit rather than down at the ant lion. It is hard to know what the ant ‘intends’ from a neurological perspective, but collectively the behaviors of the ant suggest that the mandible strike is being used to escape a threat.”
Read the entire study at PLOS ONE: “Mandible-powered escape-jumps in trap-jaw ants increase survival rates during predator-prey encounters”.