World’s loudest creature (for its size)

June 30, 2011 • 5:05 am

Alert readers Diane G. and Ray P. called my attention to a new paper in PLoS ONE by Soeur et al. that reveals the loudest known creature for its size on Earth.

What is it?  It’s a water boatman of the species Micronecta scholtzi. These are in the Hemiptera (“true bugs,” remember?).  It’s tiny—only 2 mm long (the size of Lou Jost’s orchid)—and inhabits streams in Europe. Here’s one:

What’s the big deal?  These insects produce the loudest sound per unit length of any known species on Earth. Scientists captured some in a river in Paris and recorded them underwater in the lab using a hydrophone.  Only the males make noise, a clue that the song serves a sexual function.

How loud are they? The authors note: “SPL [sound pressure level] values of M. scholtzi were compared with the values reported for 227 other species (2 reptiles, 3 fishes, 24 mammals, 29 birds, 46 amphibians and 123 arthropods) collected from the literature (Table S1).

The song consists of three parts, and the third, the loudest, can be as large as 105 decibels! That’s as loud as a power mower from three feet away, and a level that, if inflicted constantly, could cause permanent hearing loss.

Is it really the loudest animal on earth?  Yes, if the volume is scaled by a measure of body size (length). As the article notes:

. . .  the most striking feature of the song is its intensity. The song can be heard by a human ear from the side of a pond or river, propagating across the water-air interface. Estimating the sound intensity at a distance of one metre reveals a value of ~79 dB SPL rms. When considering peak values, i.e. the loudest part of signal, the intensity can reach 100 dB SPL. Whilst these values are far below those estimated for large mammals such as dolphins, whales, elephants, hippos, or bison, when scaled to body size, M. scholtzi has the highest ratio dB/body size. Even if such comparison might need to be adjusted with corrections taking into account different recording methods and conditions, M. scholtzi is clearly an extreme outlier with a dB/body size ratio of 31.5 while the mean is at 6.9 and the second highest value is estimated at 19.63 for the snapping shrimp S. parneomeris. This water bug might be the exception that proves the rule that stipulates that the size and the intensity of a source are positively related. This departure from the rule is apparent within the group of stridulating animals. In this sub-sample, M. scholtzi is identified as an extreme outlier. No other recorded animals rival M. scholtzi. Two other arthropods were also identified as outliers; the Australian miniature cricket C. canariensis [27] and the Praying Mantis M. religiosa [28].

Well, what’s the real loudest animal on earth? If you don’t scale by body size, it is a whale and a monkey in the aquatic and terrestrial realms, respectively. The National Zoo says this:

Blue whales’ low-frequency pulses are as loud as 188 decibels—louder than a jet engine—and can be detected more than 500 miles away. On land, the loudest animals are howler monkeys, whose howl can be heard three miles away.

How and why do they make this noise? The males rub their penis against their abdomen. The authors theorize that “runaway sexual selection” due to competition by males for females has made the song so loud. But there are other forms of sexual selection not mentioned by the authors, like “sensory exploitation” (females pre-adapted to respond to such songs), that could also explain the evolution of such loud songs. There are many forms of sexual selection and it’s very hard in a given case to figure out which has operated.

You can hear the sounds of these insects by clicking on a BBC Nature piece, “‘Singing penis” sets noise reord for water insect.

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Sueur J, Mackie D, Windmill JFC, 2011. So small, so loud: Extremely high sound pressure level from a pygmy aquatic insect (Corixidae, Micronectinae). PLoS ONE 6(6): e21089. doi:10.1371/journal.pone.0021089

24 thoughts on “World’s loudest creature (for its size)

  1. This is amazing — I’d say “incredible”, except for trusting the sources…

    I’m not a biologist, but a recording engineer, and as such I have at least a rudimentary understanding that to make sound, you have to push around molecules of whatever medium you find yourself in; and to make a loud sound, you have to push a lot of molecules!

    From the BBC article:
    “What makes M. scholtzi extraordinary is that the area they use to create sound only measures about 50 micrometres across, roughly the width of a human hair.”
    So how is it possible to produce more than a tiny amount of sound from such a tiny organ? It smacks of the “scientists prove that bumblebees can’t fly” folktale.

    Can anybody explain how these bugs do it?

  2. I was bemused by the statement that they found the insects in “a river in Paris, France” – did they mean the Seine? I checked in the article, and they say the same thing, and contrast this with a pond they collected another sample from. But *which* river? There are other rivers in Paris – for example the Bièvre, which runs into the Seine, but which is in a tunnel throughout its run through the city. As far as I know, the only open river in the city itself is the Seine. Is this the river the authors coyly refer to? Odd they weren’t more precise.

  3. Why do the authors use dB to make this comparison? Doesn’t comparing a logarithmic scale to an absolute measure of length make these calculations invalid?

    My math says that the whale, at 188 decibels, is about 200 million times louder than this thing at 105 decibels. Compare that to the ratio of body lengths, 30 meters for a whale and .002 meters for this creature, and the whale is only 15,000 times as long. So isn’t the whale much louder when scaled for body length?

    I’d say that mass would be a more appropriate measure than length anyway. I assume that the water boatman would win when scaled to mass.

    1. That’s a great point! Perhaps they made a mistake, although one might reply that they’re basing it on perception, and the perception of loudness is also logarithmic, so a whale would only sound, say, ten times as loud, but it would appear thousands of times larger.

    2. I too was going to question the scaling of sound intensity to body length. There’s no logical reason for it other than to calculate a gee-whiz factoid.

  4. I really hate that “the exception that proves the rule” quote. I had never heard of it before I read the book, “Dictionary of Misinformation”, which had an entry on it.

    Since then I’ve only come across it once or twice (once on a children’s cartoon), but as we all (should) know, the exception DISproves the rule. (Given “All crows are black”, and you find an albino one, then that proves that all crows are not black)

    I wish those that should know better would stop using this misleading quote so that it completely disappears from common usage.

    1. IIRC, it stems from an older meaning of “prove,” one that means “to test.” But I’m sure you knew that.

      IME its use is extremely common, so I wouldn’t place any money on the odds of it disappearing anytime soon.

  5. I’m curious why they chose to scale volume by body length for comparison purposes. Surely the ability to push air (or water) around scales with surface area, not linear dimension.

  6. “The exception that proves the rule” harks back to the older meaning of prove, which was to test.

    Probably the most annoying loud animals are some tree frogs, which can really spoil people’s enjoyment of the night.

    1. Whatever you do, DO NOT try it, as when you come before the judge it will sound rather a feeble excuse!

  7. Mantids make noise? I’ve raised several species, and I’ve never heard them make any sort of sound, nor have I ever read about any sort of mantid mating call.

    1. Anybody able to read the reference? I can’t. I know that many mantids can hear ultrasonic bat calls, so maybe their mating calls are also ultrasonic.

      1. One of the references is Gerald Durrell’s “My Family and Other Animals” (1956) which I confess I have never read. I knew (when his family lived on Corfu) that he kept mantids & chameleons among many other creatures…

        1. Oh, I read that sometime in the mid 70’s–along with some of his other books. I remember enjoying them quite a bit, and, Philistine that I am, much preferring his books to his brother’s.

  8. On land, the loudest animals are howler monkeys, whose howl can be heard three miles away.

    There’s loud and then there’s loud…I’ve heard both howlers and macaws let loose, and I’d much rather be standing next to the former than the latter at such times. Something about those higher pitches is just a lot more painful…

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