Key points
- Aquatic insects, aka waterbugs, are major biological contributors to freshwater soundscapes.
- Seven thousand species of aquatic insect produce sounds globally.
- Our bioacoustic expert takes to the water to put waterbugs on the global map.
Imagine this: you're walking down to a dam at sunset on a balmy Australian afternoon.
Your senses are alive. You feel the heat on the back of your neck, from the last rays of the setting sun. The eucalyptus smell of a nearby gum fills your nostrils. Then, there’s the sound of the native inhabitants. You hear birds screeching in flight as they swoop in to take an afternoon drink, the plucking banjo sound of a Pobblebonk frog's mating call, and the annoying buzz of a mosquito ready to bite.
The wildlife choir is noisy on this afternoon but beneath the water’s surface is one of the most underrated parts of this soggy symphony.
Cue the waterbugs.
Warbling waterbugs heard around the globe
According to scientists, aquatic insects or ‘waterbugs’ are major biological contributors to freshwater soundscapes.
However, their identity in Australia and even globally, has largely gone unrecognised,along with the sounds they make. There are few spotlights on these wonderous warbling waterbugs – they’re more the singing in the shower types.
A new international paper published this month in the prestigious Proceedings of the Royal Society of London journal explores the potential of acoustic monitoring of aquatic insects. Researchers from Australia, England and France set out to estimate the potential number of sound-producing aquatic insects worldwide. They used data from the Global Biodiversity Information Facility. Led by Camille Desjonqueres from Grenoble University in France, they found that four aquatic insect (or waterbug) orders totalling more than 7000 species produce sounds globally. The main group to contribute to these sounds are aquatic beetles.
One well known member of the aquatic beetle group is the water boatman. He’s a little guy with a big chirping voice. They can often be seen zooming around the top of a pond or dam. Another favourite is the whirligig beetle. He makes a rubbing sound like a fingernail being dragged across a comb. Usually spotted in groups, whirligig beetles get their common name from their habit of swimming rapidly in circles when alarmed.
Recording the best bug voices
Despite the global estimate of 7000, the number of waterbugs that sing is likely to be much larger. We have our poor knowledge of aquatic insect bioacoustics to thank for that. It's something our researchers are keen to fix!
Dr Simon Linke is our bioacoustics expert and co-author of the paper. He is familiar with using sound recorders in trees to record the sounds of frogs. In fact, we wrote a whole ‘loved up’ article about his work with frisky frogs in the Murray-Darling Basin. He believes the same passive acoustic monitoring (PAM) methods can be used to record the sounds of waterbugs effectively and efficiently.
Waterbugs are a major indicator used to assess the ecological condition of freshwater environments. However, current methods to collect and identify aquatic insects require advanced taxonomic expertise and rely on invasive techniques. Yes, unfortunately we are talking about a sudden (yet humane) death to enable scientists to study the little musical mites. In contrast, PAM methods allow the waterbugs to stay alive and in their own environment. They can also record a continuous signal from a water area and not just a snapshot at one point in time.
A waterbug's life
“Insects are a good indicator of certain water chemicals and parameters. There’s a whole bunch of water insects like mayflies, stoneflies and caddisflies that make the little cases. They can help us determine the make-up of the water,” Simon said.
However, he warns the presence of singing waterbugs does not always indicate “good” water quality. Unlike frogs, who belt out a croak to attract a mate to a good quality waterway, waterbugs can be quite non-judgemental performers.
“For a start not all waterbugs sing and the insects don't care whether the water quality is categorically good or bad. They care how many nutrients are in the water and how warm it is,” Simon said.
“Good quality water usually has low nutrients and is cooler. Whereas what one might describe as bad quality water has less flow, less oxygen and more nutrients. For example, if you put in a dam, the dam warms up and there's other nutrients coming in.”
To help with the acoustic and environmental analysis, the researchers broke down two different typologies of rivers where the interpretation can be different.
All quiet on the water front
“A good quality mountain stream is usually fairly silent. And once you degrade it, it becomes noisier. Whereas a tropical stream (which might have good or average water quality) is always noisy. Typically, it always has these water beetles and these waterbugs that indicate high nutrients and warmer temperature,” Simon said.
Waterbugs living in either extreme environments – water ways with really good quality water or really bad water quality – will be quieter or even silent.
“So, the waterbugs don't pass judgement on whether it's a good or bad water quality. They are indicators of high nutrients and usually temperature and flow,” Simon said.
Despite waterbugs having similar responses in pristine and degraded environments, Simon believes they are still useful to evaluate ecological conditions. He predicts that the sites with the most acoustic activity and richness will be sites at intermediate environmental conditions. Typically this means warm water, medium level nutrient input and low flows.
The research aimed to build a baseline to study and categorise freshwater environments using acoustic waterbugs. Both expert and automated identifications will be necessary to build international reference libraries and to conduct acoustic bioassessment in freshwaters.
So, the quest to better categorise waterbugs across the globe has begun. In the meantime, you can appreciate their tiny tenor talents by strolling down to you nearest waterway.
Music to your ears
You can listen to Simon's recording of a billabong at midnight in far north Queensland that features the high pitch chirp of little water boatman MP3 (802 KB). Or treat your ears with the sound of the creaky whirligig beetle. MP3 (263 KB)