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First published online November 17, 2006
Journal of Experimental Biology 209, iv (2006)
Copyright © 2006 The Company of Biologists Limited
doi: 10.1242/jeb.02577
Outside JEB |
BOUNCING BITES
University of Guelph
dfudge{at}uoguelph.ca
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In the children's poem The Ants at the Olympics by Richard Digance, ant athletes get no respect. According to the poem:
`At last year's Jungle Olympics, the Ants were completely outclassed. In fact, from an entry of sixty-two teams, the Ants came their usual last...'
The poor ants don't win any medals because they have to compete against the hippos in the shot put and the cheetahs in the sprints. Too bad there were no events such as `fastest predatory strike' or `highest acceleration of an appendage,' because trap-jaw ants would win gold every time.
In a recent paper in Proceedings of the National Academy of Science, Sheila Patek and colleagues report the results of a biomechanical study of jaw-closing in trapjaw ants. They found that these ants use their jaws to carry out some truly remarkable and downright athletic feats.
Trap jaw ants are known for their absurdly large jaws that they use in fast predatory attacks. Patek and colleagues wanted to investigate the jaw-closing event using an ultra-fast video camera, because previous attempts with slower cameras were unable to resolve the entire event. The team was also interested in documenting other lesser-known uses of the jaw-snapping such as fending off intruders and escaping predators.
To do this, Patek and her coworkers carried out a series of experiments with a high speed video camera that could capture 5x104 frames per second. This allowed them to describe the details of jaw closing, and investigate whether the ants used their explosive jaws to propel themselves and/or intruders, and if so, how.
They found that the jaws close with an average velocity of 38.4 m s-1, which gives trap-jaw ants not only the gold medal, but also the world record for the fastest movement generated by any organism. Falcons can drop out of the sky at far greater speeds, but they have gravity on their side. Trap-jaws pull off their feat using only stored internal energy.
Getting the mandibles up to 38.4 m s-1 in just 100 ns requires incredible acceleration, in this case, 105 g, which is exceeded only by the discharge of cnidarian nematocysts. The researchers also calculated that closing jaws can exert 47 mN of force, or about 400 times their own body weight. While this kind of force is certainly adequate to incapacitate prey, it is also enough to launch an ant into the air if the force is directed against something massive.
The researchers found that the ants indeed launched themselves in the air when confronted with potential threats, and they did so with two distinct behaviours - one they used to repel intruders (called a `bouncer defense'), and another that they used to escape predators (called an `escape jump'). The bouncer defense was instigated by firing the jaws against an intruder, which had the effect of sending it and the ant off in opposite directions. The escape jump was elicited by directing the jaws down at the ground, sending the ant flying in the air, and presumably out of harm's way.
Watching the supplementary online videos for this paper is strangely entertaining. In slow motion, one gets to watch the ants launch themselves into the air, all the while spinning at the impressive speed of 63 rev s-1. It's enough to make an Olympic gymnast or figure skater jealous - until you see the landing.
References
Patek, S. N., Baio, J. E., Fisher, B. L. and Suarez, A. V.
(2006). Multifunctionality and mechanical origins: Ballistic jaw
propulsion in trap-jaw ants. Proc. Natl. Acad. Sci.
USA 103,12787
-12792.
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