The movements of organisms like worms in the soil create distinctive sound patterns
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It may not have the appeal of a dawn chorus of birds, but the noises of ants, beetle larvae and worms recorded below ground can provide a snapshot of whether an ecosystem is healthy.
“The idea is that we can monitor soil health from the sounds the invertebrates are making,” says Jake Robinson at Flinders University in Adelaide, Australia.
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He and his colleagues chose six locations at Mount Bold reserve, a 55-square-kilometre area around a reservoir south of Adelaide, to make 240 recordings over five days in spring 2023, each lasting for 9 minutes.
Two sites had been cleared of trees about 15 years earlier and were being kept as grassland, two had been cleared but trees and bushes had been growing back for about 15 years, and two were undisturbed grassy woodland.
Robinson and his colleagues also dug up soil samples at each location and put them in containers, which they placed in sound attenuation chambers, devices that allowed the noises from the soil to be recorded in controlled conditions with other sounds excluded. Then the researchers worked through the soil samples to count the type and number of invertebrates in each.
Jake Robinson (left) and his colleagues listening to noises in the soil
Traci Klarenbeek
They found that undisturbed and revegetated plots had more soil invertebrate species, including organisms such as beetle larvae, worms, centipedes, woodlice and ants, and a higher abundance of specimens generally than cleared plots.
To analyse the noises, Robinson and his colleagues used a sound complexity index that works on the premise that many biological actions, such as millipedes moving, produce a characteristic sound pattern.
A lot of varied sound activity will mean a higher index score and hence that more types of organisms are present. The soil from the sites with regrown vegetation had a 21 per cent higher index score than that from cleared sites.
