Dr. Jérôme Sueur, Muséum national d'Histoire naturelle, Paris
It is the tiny water boatman which can make a noise of almost 100 decibels.
ScienceDaily (July 1, 2011) — 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.
The frequency of the sound (around 10 kHz) is within human hearing range and Dr. James Windmill of the University of Strathclyde, explains one clue as to how loud the animals are: "Remarkably, even though 99% of sound is lost when transferring from water to air, the song is so loud that a person walking along the bank can actually hear these tiny creatures singing from the bottom of the river."