Using its penis, a flea-sized insect makes a noise as loud as a lawnmower.


- The loudest sound created by an animal, relative to its size, has been recorded.

- The flea-sized water boatman produces sounds as loud as a lawnmower by stroking an appendage on its abdomen against its penis.

- The research could inspire miniaturized sonar for unmanned underwater vehicles.

Supporting the notion that it's not the size that counts, researchers have recorded the loudest sound ever produced from an animal when adjusted for its body size. The water boatman, a tiny aquatic insect about the size of a flea that lives on the bottoms of rivers and ponds, uses its minuscule penis to produce chirps as loud as a lawnmower.

The boatman makes the sounds by rubbing a special sound-producing appendage on its abdomen against its penis. How the tiny appendage -- only 50 microns long -- can produce so loud a sound remains a mystery.

Click here to listen to the boatman's call, scroll to "NEW! PYGMY WATER BOATMAN "

The findings signify more than just the novelty of an insect stroking its private parts extremely loudly. James Windmill, one of the researchers who made the discovery, notes that a better understanding of the discovery could lead to new acoustic devices like smaller sonar systems for unmanned underwater vehicles or miniaturized ultrasound probes for medical applications.

Sueur and colleagues David Mackie and Windmill, engineers at the University of Strathclyde in Glasgow, Scotland, began to investigate. They published their results in the journal PLoS ONE.

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"We had a bit of trouble to start with because we thought the sounds were coming from relatively larger insects because the sounds were so loud," Windmill told Discovery News. "After bringing insects into the lab, we figured out it was this one."

The fact that people along the water's edge can hear the sounds indicates just how loud they are. Only 1 percent of sound released in water is transferred into the air above.

The researchers recorded the boatman making a series of chirps that peaked at 99 decibels. Adjusted for the insect's tiny size, this is the loudest sound produced by any animal.

Typically, larger animals make louder sounds.

"This small aquatic insect constitutes a major exception to this rule," said Fernando Montealegre of the University of Bristol, U.K.

The loudest sound ever recorded in an absolute sense was a 236-decibel burst from a sperm whale.

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How the insect creates this loud sound is still a puzzle. The water boatman carries a bubble of air with it underwater to breathe.

"It's possible that they're using that to amplify the sound, and the bubble is actually acting as a sort of resonating loudspeaker," Windmill said.

It could also be using its entire body as an amplifier, he added. Crickets use their wings to amplify their vibrations.

Another mystery is why the animals bother to call so loudly. The researchers suspect the reason is "runaway sexual selection" -- that nearby females are more likely to hear them the louder they shout, and that they will out-sing competing males.

Other animals perhaps have to balance the benefits of singing loudly with the risk of attracting a predator.

"We're pretty sure that there is no predator listening for the sound that these guys are making," Windmill said, leaving them free to turn up the volume with no downside.