At the last instant before the bat snatches the insect out of the air, the mantis goes into what Yager calls a "power dive"heading straight for the ground.
"When they hear a bat they keep flying, but they fly in a sudden downward spiral that helps them avoid capture," Yager says. The power dive results in a safe getaway about 80 percent of the time.
Many other insectsincluding grasshoppers, green lacewings and tiger beetleshave evolved a bat countermeasure: "the bat sensitive ear," as researchers say.
But Yager's work "pushes the envelope," says Brock Fenton, a bat specialist at York University in Toronto, Canada. "He's investigating how the detector actually works."
The National Institutes of Health and the National Science Foundation fund Yager's research. He will present his most recent findings at the First Pan-American/Iberian Meeting on Acoustics, in Cancun, Mexico, next month.
Praying Mantis Surgery
The attack sequence of ultrasonic cries that the bat emits is very complex, Yager says. He was intrigued by the mantis' ability to gauge the precise moment of attackand then to dodge. Yager wanted to "get inside the animal's head and hear what the mantis hears," he says.
Yager and graduate student Jeffrey Triblehorn invented a surgical procedure to implant electrodes into a mantis' head.
The electrode is wrapped around the insect's auditory nerve. When the mantis hears the bat's ultrasonic cries, the ear sends a signal to the brain via the auditory nerve.
After a few days to let the newly wired mantis recover, the researchers suspended it from the ceiling by a tether in the middle of a dimly lit "flying room."
Then they released a batand observed the attacks via high-speed video and ultrasound detectors.
Yager and Triblehorn determined that the mantis perceives the increased rate of ultrasonic pulsesand calculates the right moment to dive.
The team has also found that 300 milliseconds before the bat hits the mantis, the insect's auditory nerve goes completely dead.
"This is the time you would expect the nerve to be going crazy," says Yager. Yager suspects that the nerve shuts down immediately after triggering the dive response.
As the mantis enters the dive, its visual system, or possibly its minuscule hairs that serve as wind detectors, may influence adjustments to the dive that the scientists call "last chance maneuvers."
The mantis, like all creatures under attack, is using every available means to save its life.
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