Cabinet of Freshwater Curiosities: tiny freshwater insect is the ‘loudest animal on Earth’

If you’re a long-time follower of the Freshwater Blog, you might remember our Cabinet of Freshwater Curiosities project from more than a decade ago. That website has since washed away down the rivers of time, but we thought it was the right moment to showcase our collection of curious freshwater plants and animals again. So keep your eyes peeled over the coming months as we dust off the Cabinet and celebrate the wonderful world of freshwater life!

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This month’s entry into the Cabinet of Freshwater Curiosities is the lesser water boatman – Micronecta scholtzi – a common European freshwater bug that produces a peculiar courtship song by rubbing its penis along its abdomen, a sound which reaches an incredible 99.2 db!  That’s a sound level equivalent to sitting in the front row of an orchestral concert, or standing close to a passing train!

As Dr James Windmill at the University of Strathclyde – a lead researcher on the June 2011 study “So Small, So Loud: Extremely High Sound Pressure Level from a Pygmy Aquatic Insect” – describes, “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.”

Micronecta means “small swimmer”, and their sound, used by tiny (2mm) males to attract mates, is produced by rubbing its ribbed penis across its abdomen, in a process called stridulation. In the lesser water boatmen the area used for stridulation is only about 50 micrometres across, roughly the width of a human hair. 

This stridulation process is similar to that used by grasshoppers and crickets to produce their idiosynchratic chirps and chirrups. Dr Windmill continues, “If you scale the sound level they produce against their body size, Micronecta scholtzi are without doubt the loudest animals on Earth.”

The loudest human shout ever recorded is 129db by British teaching assistant Jill Drake in 2000.  Sperm whales have been recorded emitting sounds reaching an incredible 236db, a cacophony required to communicate across vast, turbulent oceanic distances.  Decibels are a measure of the intensity or ‘loudness’ of a sound, measured on a logarithmic scale.  This means that for every increase of 10 decibels, there is a 10 fold increase in sound energy.

By comparison, a normal human conversation is generally measured at around 60db.  Incredibly, at 99.2db, the sound made by the lesser water boatman is almost 10,000 times more powerful – akin to a car horn, power tool or passing train.

The researchers say their findings demonstrate how aquatic animals such as the lesser water boatman have evolved to be able to communicate in underwater environments. In this case, they highlight how their loud stridulations help the male insects to find a mate.

This remarkable little bug shows that remarkable creatures often live in the most everyday freshwater environments. So next time you’re walking along your favourite river or lake, stop for a moment to listen – you may be surprised what you can hear!