As so often happens, a headline caught my attention while I was perusing the online edition of ScienceDaily (July 1, 2011). 
And the winner is… The Lesser Water Boatman!
The article states, “Scientists have shown for the first time that the loudest animal on earth, relative to its body size, is the tiny water boatman, Micronecta scholtzi. At 99.2 decibels, this represents the equivalent of listening to an orchestra play loudly while sitting in the front row.”
Others have compared it to the volume of a passing freight train.
And when they say tiny, folks… I’m here to tell you, they mean tiny! Two millimetres. That’s it.
So, how does this little pipsqueak come up with The Big Sound? I am SO glad you asked!
Science Daily puts it this way, “The song, used by males to attract mates, is produced by rubbing two body parts together, in a process called stridulation. In water boatmen the area used for stridulation is only about 50 micrometres across, roughly the width of a human hair. “We really don’t know how they make such a loud sound using such a small area,” says Dr. Windmill.”
Thinking that perhaps the writers at Science Daily were being a bit coy, I tried to look up exactly what was rubbing against what. Wikipedia failed to disappoint! “M. scholtzi is easily differentiated from other species in this genus by the twisted left paramere of the male genitalia… The male of this species produces its underwater courtship song by stridulating a ridge on its penis across corrugations on its abdomen, the area involved measuring only 50 micrometres across, or about the thickness of a human hair. “
The boys at Wired Science put it rather more bluntly, “Bug’s Penis Makes Loudest Animal Sound“!
As we say down in central Arkansas, ‘yew jus’ cain’t make this shit up’!
 Special thanks go out to my dear friend, Kelly, who introduced me to Science Daily.