As you may have noticed, I’ve got a lot of ‘favorite’ ants. Well, here’s another – Odontomachus clarus, the Trap-jawed Ant. Their mandibles are elongated, like a set of tongs. They can ‘cock’ their jaws in a wide-open gape. As the ants open their jaws, the ant’s huge jaw muscles stretch tendons in the ant’s head capsule. Then the ant will ‘lock’ her jaws open using an internal latch system, leaving her tendons in this taught, stretched condition. Sort of like a crossbow.
When the ant triggers her jaws, she releases the internal latch and the energy stored in the tendons gets released all at once. Her stretched tendons slam her jaws together much more quickly than if powered by the relatively slow contraction of muscles.
The ants have a set of spikes at the end of their mandibles, and these spikes slam into her target if the ant is fighting or hunting. Or the ant may point her jaws at a relatively immovable object, such as the ground…then the force of the jaws closing throws the ant through the air, away from danger.
These wonderful ants are an example of creatures that I had read about, but never expected to see. But then my friend Gordon Snelling showed me an Odontomachus clarus nest when we were in the Whetstone Mountains…I was giddy over it. I honestly thought I’d pee myself with excitement.
Unfortunately, my photography skills were not adequate to the task of getting good shots of those ants. I did get a photo of the nest, but my ant photos were just unusable blurs.
So I was extremely excited to later stumble across foraging Odontomachus clarus workers in my Tucson housing area one night in June, 2004. The ants were slowly picking their way through the crushed gravel, twigs, and fallen leaves beneath the ornamental vegetation outside of the Community Center.
These are very pleasant ants to watch. They are reasonably large, perhaps a half inch or so long. They are not very shy, and they are not overly aggressive. When they are hunting, they moved slowly, deliberately. They would put their antennae and their head between pebbles, or under leaves, looking for prey. They seemed to be stalking. They would pause frequently, as if waiting for prey to move.
Watching the Odontomachus workers made me think of the stalking behavior of the Velociraptors in the movie “Jurassic Park”. I think it’s because of the way the ants would turn their heads to peer around corners and under twigs, then pause, as if waiting to see what would startle at their sudden appearance.
The way they used their antennae also contributed to the feeling that the ants were peering at things. They seemed to move their antennae together. Perhaps, though, they just move their antennae more slowly than other ants, so it was easier to watch them.
Some of the workers I watched had jaws that looked worn, as in the photos below.
These wokers did not have the longer/sharper processes on the tips of their jaws that other workers had. I wonder if these were older workers, and their jaws were just worn.
The ants hunted with their jaws cocked open, for the most part. It was interesting that they were able to de-cock their jaws slowly when they wanted to. I would have expected that it would take a lot of energy for them to cock and un-cock their jaws, so that they might hesitate to do it. But that didn’t seem to be the case, they toggled between cocked and un-cocked states often and easily.
They would also move the two jaws together independently. It makes sense that thy would be able to do so when you remember that their jaws are not just weapons, but tools for digging, brood care, and all of the other tasks ants normally perform.
I mentioned earlier that there were trigger hairs at the base of the worker’s mandibles. These hairs let the ant gauge exactly when to snap its jaws shut. The trigger hairs are very visible in the photo below.
The trigger hairs make sense when you consider that the tips of the jaws will be the fastest moving parts when the jaws slam shut. If the impact of the jaws on prey is a millimeter or two closer, the impact on the prey won’t be as great, and the spikes on the tips of the jaws won’t hit the prey. A millimeter too far away, and the jaws will miss the prey entirely.
So the jaws are, in a sense, a ranged weapon. The ant needs to get the distance just right, and that’s where the long trigger hairs come in.
In addition to getting the distance right, the ants also need to get the angle just right.
I wonder if this need is related to the way Odontomacus move their antenna. I’ve mentioned that they move their antennae slowly, deliberately, and usually together. I think that they use their antennae to position themselves accurately with regard to their targets. If the ants are not perpendicular to their target when they strike, then their target isn’t going to receive a full-force blow from the jaws. And moving their antennae slowly, deliberately, and together helps them get their jaw orientation just right.
What spectacular little creatures these are.
Sources:
Wulfila Gronenberg, Jürgen Tautz, Bert Hölldobler. (1993). Fast Trap Jaws and Giant Neurons in the Ant Odontomachus. Science 22 Oct 1993: Vol. 262, Issue 5133, pp. 561-563.
S. N. Patek, J. E. Baio, B. L. Fisher, and A. V. Suarez. (2006). Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants. PNAS August 22, 2006 103 (34) 12787-12792.
Yang, Sarah. (2006) Ant jaws break speed record, propel insects into air, biologists find. This is an article summarizing the previously listed Suarez paper.
