Praying Mantis Uses Ultrasonic Hearing to Dodge Bats
Bijal P. Trivedi
National Geographic Today
|November 19, 2002|
To avoid attack by a bat, one of its main nocturnal predators, a praying
mantis maneuvers like a fighter pilot in aerial combat.
"Fighter pilots and mantises have evolved the same strategyand that fact speaks to its strength," says David Yager, a neuroscientist at the University of Maryland, in College Park, whose laboratory studies the interactions of predator and prey.
Under attack by a bat, a praying mantis suddenly dives straight toward the ground.
To illustrate the defensive maneuver for his students, Yager shows a clip from "Top Gun." "The mantis uses the same strategy as Tom Cruise," he says.
When Yager first documented the praying mantis' moves, fighter pilots called to confirm that they had defended themselves the same way.
The airborne combat between bat and mantis is primal. The large slender carnivorous insect, with its two grasping legs, freely moving head and bulbous eyes, relies on its own ultrasound detector to warn of bat attacks.
Bats emit a series of ultrasonic pulses that bounce back from surrounding objects, including prey. The bat uses these reflected signals for orientation and as part of its sonar system to detect food.
As the bat nears prey, it increases the rate of these calls, eventually climaxing in a "feeding buzz" as it prepares to strike.
Although ultrasound helps the bat find its prey, it also helps the prey find the bat.
The praying mantis' ultrasonic hearing picks up frequencies above 20,000 hertzjust beyond the range of humansthrough a single ear located in the center of its chest.
Yager made a name for himself by discovering the mantis ear while he was a graduate student at Cornell University, in Ithaca, New York.
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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