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The fastest jaw in the west.

The blink of an eyes is as slow as molasses compared to the bite of the trap-jaw ant. Eyelids can take a third of a second to shut and open. But the jaws of at least one species of these specialized ants, Odontomachus bauri, work 1,000 times as fast, says Wulfila Gronenberg, a neurobiologist at the University of Wurzburg in Germany. The fastest strike observed took 0.33 millisecond (ms), beating out other record movements such as the release of stingers by hydrozoans (jellyfish) at 0.5 ms or the escape jump of click beetles at 0.6 ms.

The group studied ants fixed in position from their middle segment back. In addition to filming the jaws, the scientists traced the nerves involved and projected the view of this motion through a microscope onto a screen, where they could monitor the movement with sensitive photo cells, Gronenberg explains. Those measurements show that the jaws reach a peak speed in mid-snap, then slow down, perhaps to protect the jaws in case they collide.

These ants came from Arizona, but their relatives populate warm regions throughout the western hemisphere.

The ants approach prey with their 1.8-millimeter-long jaws cocked wide open, says Gronenberg. The first detect prey with their antennae, then jerk forward so that the target rubs against the ants' 1-mm-long "trigger" hairs, two of which are located along the edge of each jaw. This contact causes the jaws to snap shut, Gronenberg's team reports in the Oct. 22 SCIENCE.

He and Wurzburg colleagues Jurgen Tautz and Bert Holldobler discovered that these hairs are touch-sensitive nerve endings. Using special stains, the researchers traced these endings back to nerve cells. Very large fibers, or axons, extend from these nerve cells to the part of the insect's brain that controls the mouth.

"The whole system works as a single unit," says Gronenberg. Touching any one trigger hair sets off both jaws. The large diameter or the axons indicates that they transfer information very quickly. Motor nerves that reach from the brain to the jaw muscles lie right next to these axons, suggesting that they connect with the axons, creating a direct reflex.

These motor nerves activate muscles that may release the joints that have kept the jaw open, says Gronenberg. The team observed that the big "closer" muscles are active electrically before the jaws snap but not during the motion. "This is like the cocking of a spring, like a catapult," Gronenberg explains. Apparently, a smaller muscle rotates a jaw joint to release the energy stored in the closer muscles and snap the trap.
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Title Annotation:Odontomachus bauri trap-jaw ant snaps jaws shut in .33 milliseconds
Publication:Science News
Article Type:Brief Article
Date:Nov 6, 1993
Previous Article:Miranda: shattering an old image.
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