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Jaw-dropping antics

August 21, 2006 By Narelle Towie This article courtesy of Nature News.

Ants escape danger by snapping their jaws.

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When trap-jaw ants need to get out quick, they use their heads, not their legs to escape. This large species of Costa Rican ant smashes its jaw into the ground, causing the ant to catapult up and away from danger.

Videos of Odontomachus bauri show that this ant can propel itself 8 centimetres up into the air using jaws that snap shut at a speed of nearly 65 metres per second perhaps the fastest predatory strike measured.

Brian Fisher of the California Academy of Sciences, San Francisco, and colleagues filmed the ants to help settle a lab bet about whether it was faster than the mantis shrimp, which flails its club-shaped front leg at peak speeds of 23 metres per second to shatter the hard shells of its prey.

The team used a high-speed video camera to film seven trap-jaw ants in action at 50,000 frames per second ( see videos). The results were a surprise. "We found that the jaws were closing at triple the speeds previously thought," says Sheila Patek, a biologist and co-author on the paper. The team's results are published in the Proceedings of the National Academy of Sciences1.

The snapping jaw gives the ants a bizarre multi-purpose tool for hunting and defence. The ants often approach other insects with their jaws cocked open. Snapping them shut can both give the ant a quick escape and also knock down the combatant, stunning it so the ant can come back with a successful attack.

The ant can also cock its head sideways and strike its mandible against the floor. The impact shoots its body upwards for nearly 0.3 seconds long enough to avoid the tongue of a hungry lizard before it lands haphazardly up to 40 cm away.

Helped by these skills, O. bauri thrives throughout Central and South America. They are amazing because of the way they work together to stay safe, says Fisher. "A group of ants can confuse predators by performing multiple, simultaneous escape jumps, creating what I call the popcorn effect."

Snap shot

The snapping speed is achieved in much the same way as a mousetrap. An ant cranks its mouth open by slowly contracting one set of muscles, and then holds it open with a couple of latches. When sensitive nerve endings 1-millimetre-long hairs along the edge of the jaw are touched, the latches are released, and other muscles slam the jaw shut 2,000 times faster than the blink of an eye.

The movement is faster than a cheetah's run (which can ramp up to 20 metres per second in under 2 seconds), or a jellyfish's throw of a lethal dart, clocked at an average of 14 metres per second. But it's slower than the dive of a peregrine falcon, which exploits gravity to reach speeds of 75 metres per second.

O. bauri is not the only species of ant to use snapping jaws to snare prey, but it does seem to be the only one who uses the trick to perform escape jumps.

The researchers now hope to discover how the trap-jaw mechanism evolved across other ant genera, to see if other species are also capable of jumping to safety.

"We have a lot to do," says Patek. "One major area of interest is to understand how and when the ants fire their mandibles in different context. How do they decide to attack a large predator and bounce off it instead of directing their strike against the ground and propelling themselves away?"

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References

  1. Patek S. N., Baio J. E., Fisher B. L.& Suarez A. V. PNAS, 103. 12787 - 12792 (2006).

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