Eastern bared bandicoot
Charles Darwin fundamentally changed how we see ourselves as human creatures by listening to evidence laid out by the animals that surround us. The beaks of different finch species that populate the Galápagos Islands told the astounding story of speciation and adaptation. But before, during and after the study of finches there were earthworms, and following the publication of “Origin of the Species”(1859) came”The Formation of Vegetable Mould through the Action of Worms, with Observations on Their Habits” (1881). This book was a bestseller, gathering the results of four decades of study, Darwin having first published on worms in 1837.
Darwin was following a hunch that soil fertility was a product of bioturbation, now specifically called biopedturbation since there are now half a dozen different categories of bioturbation recognised. The added “ped” refers specifically to the mixing of soil by animals. It’s also possible to mix marine sediments, etc.
Apart from exploring fundamental ideas about the nature of life, Darwin also succeeded in bringing ideas to public attention by arousing curiosity and involving others in his research. Darwin might have also started the first citizen science project by appealing for worm casting data from collaborators around the globe.His family members collected data on worm castings for him and went to the extent of conducting experiments testing the hearing of worms by playing musical instruments of different types. Worms turn out to be deaf.
Among many findings, Darwin calculated that worms in his locale were responsible for moving soil to the surface of a paddock in the order of 160 tons per acre per year. Worms were cast as the bio-engineers of soil fertility. The stuff Darwin called ‘vegetable mould’ was the organically altered pre-digested dark soil horizon in which plant roots thrived. Worms built the fertile soils that supported English agriculture.
In Darwin’s time worms were regarded as pests, only responsible for unsightly mounds of castings. In the end, Darwin the conservationist told his son William, what he hoped his book would reveal is that ‘worms have much bigger souls than anyone would suppose’.
Darwin made the utility of ecology evident, with worms as providers of ‘eco-system services’. Bandicoots likewise are among a whole suite of small native animals that tilled the Australian soil, keeping it in better condition for supporting plant life.
In the Australian context, soil structure is markedly different to that found in rural England. It should come as no surprise that soils that are frequently dry do not support the same populations of earthworms. Nor is there generally the same rich banding of soil horizons. Yet there is still bioturbation at play, where worms are absent, ants may carry out the work of dragging stuff in and out of the ground. Or larger burrowing animals may be at work. Bandicoots have long thin snouts which they insert into the soil to sense food items, they will then dig to retrieve the food. The ground is left pockmarked as if giant earthworms were at play.
British settlers brought with them a slew of animals to recreate home. Some, like rabbits, are master bioengineers which had coevolved with foxes, digging extensive burrows for safety. Feral cats and foxes do hunt rabbits but disproportionately ravage native mammal populations. Australian small mammals have suffered the largest extinction rates of anywhere in the world during the colonial era. Three species are confirmed as extinct in the last decade.
Thirty three species of Australian mammals have been lost since settlement. This includes four distinct species of geographically isolated barred bandicoots. Specimens remain only in museum drawers. The Eastern barred bandicoot once found on the mainland is now restricted to Tasmania where foxes are absent.
Other bandicoot species perhaps with greater ability to seek cover from predators will still emerge from bushland or from underneath buildings to dig holes into paddocks or lawns seeking a meal of invertebrates, including the odd juicy worm.
The declining condition of Australian soils has created a business opportunity for those who would offset carbon emissions by increasing soil carbon sequestration. As in Darwin’s time the public are ready to have the good news explained, there are animals who usefully dig the soil and they possess a soul bigger than you may suppose.
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