Trap-jaw ants have an amazing weapon: their mouth. Their spring-loaded jaws are capable of snapping shut as fast as 60 meters/second (134 miles/hr) and can generate forces over 300 times their body weight. These ants are ferocious predators of termites and other small insects with their lethal jaw snap. Trap-jaw ants also can catapult themselves into the air with a jaw snap:

This trap-jaw ant strikes at an obstacle, flinging itself backward over its mates. Modified from Patak Lab Video, Duke University

Aside from being really neat to watch, why might ants that are so formidably protected with powerful jaws use them in such a strange way? Is it just a byproduct of robust jaws that they occasionally send themselves flying ass over teakettle?

Jaws that snap shut with extreme force can have both an offensive and defensive function. The jaws can toss an opponent away during a fight; and when under attack, a colony of ants fling themselves around like popping popcorn, disorienting attackers.

New research looked at how the jaws might function against a predator of ants: antlions. Antlions are, as you might infer from the name, a type of insect that preys upon ants. Antlions build lairs in the sand and wait for an ant or another insect to tumble in. The antlion grabs its victim with large, menacing jaws, pulls it under the sand, and injects digestive fluids into the prey’s body cavity.

If you think this sounds a bit like a Star Wars saarlac, a Tremors graboid, or the Ceti eel that got put into Chekov's ear, you aren't wrong. All of those were inspired by antlions. It is a worthy adversary for a trap-jaw ant.

Antlions fling grains of sand at their victims to make their pit walls less stable, and hurry their slide to doom:

After flinging sand at prey, the antlion grabs an ant and drags it under the sand at the bottom of the pit. Larabee and Suarez, 2015

Researchers Fred Larabee and Andy Suarez wondered if ants' trap-jaw could help defend against antlions. To find out, they dropped a bunch of ants onto a bunch of antlions, and watched what happened. This sounds a bit like what a curious kid might do, but with controls and high-speed video documenting it, it's also science.

First the researchers harvested antlions, and let them set up their pitfall traps in the lab. Then they added trap-jaw ants near the pits. About half of the time the ants were able to run away from the antlion and out of the pit. 36% of the ants were eaten. But 15% of the ants used their jaws to catapult themselves out of the pit after encountering the antlion.

Odontomachus brunneus) jumping out of an experimental antlion pit.

To make sure that the jaws were critical to the ants' escape, the researchers glued the ants' jaws shut, and compared survival with and without functioning mandibles. Ants with intact (untreated) jaws escaped at twice the rate of ants with superglue braces.

Trap-jaw ant mandibles were glued shut to prevent ants from snapping. Larabee and Suarez, 2015

Now we know that in one species of trap-jaw ant, the jaws do have a defensive function. But trap-jaws have independently evolved multiple times in ants; and not in closely related groups. Is the ability to fling themselves into the air something that is a happy accident of giant jaws, or is it also being acted upon by natural selection? And which came first, the offensive or defensive function?

By measuring strike speed, force, and the contexts of these behaviors in different ant species, researchers hope to puzzle out how these amazing structures evolved.

Larabee & Suarez. 2015. Mandible-Powered Escape Jumps in Trap-Jaw Ants Increase Survival Rates during Predator-Prey Encounters. PLOS1 doi: 10.1371/journal.pone.0124871

Spagna, et al. 2008. Phylogeny, scaling, and the generation of extreme forces in trap-jaw ants. J Exp Biol 211, 2358-2368. doi: 10.1242/​jeb.015263.

Patek, et al. 2006. Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants. PNAS 103(34):12787–12792, doi: 10.1073/pnas.0604290103