Lesser Water Boatman Micronecta scholtzi

They are some 2 mm long and are common in freshwater ponds and lakes across Europe, preferring stagnant to moderately moving water. The male of this species produces its underwater courtship song by rubbing a ridge on its penis across corrugations on its abdomen. A team of biologists and sound engineers from France and Scotland have recorded M. scholtzi producing sound up to 99.2 decibels, a volume comparable to a passing freight train. It is classified by Guinness World Records as the loudest penis.

This species is considered the loudest of all animals for its size. Despite knowing the mechanism of its sound production, researchers are still mystified by the volume produced and feel that once the process is understood, it could open up a useful avenue in ultrasonics.

A genus of aquatic predatory bugs in the family Micronectidae, who used to be a subfamily of the Corixidae.

The genus' main claim to fame is the stridulatory courtship song of Micronecta scholtzi . Which they sing with their penis. The relevant part is narrower than a human hair. The song still reachs almost 100 decibels.

Scientists are still baffled that they can make such incredible noise with such a tiny organ, which just goes to show that scientists can be very cruel.