Dirt is, in many ways, the lifeblood of our planet. We rely on soil and the particles found in it to grow our food and to keep our water clean. Nearly a quarter of the earth's biodiversity lives out their lives in the dirt beneath our feet. To recognise the importance of dirt, our planet will celebrate World Soil Day on December 5. And we here at Earth Touch are doing our part by celebrating the animals whose lives are, in some part, intimately connected with soil.
They're probably the first creatures that come to mind when you think of dirt: earthworms. The slimy, floppy critters are known as 'ecosystem engineers'. They're animals that, like us, produce incredible changes in their environments. And the effects of those changes echo throughout the rest of their environment. For the worms, that's mostly by digging holes through soil, which are called burrows, both vertically and horizontally. These burrows allow chemicals like water and oxygen to infiltrate the ground and for other compounds, like carbon dioxide, to leave.
As they munch their way through the dirt, they help organic materials – that is, dead animals and plants – to decompose, freeing up important nutrients to become absorbed through the roots of living plants, and ultimately be digested by the animals that eat those plants. According to the Earthworm Society of Britain (which is an actual thing that actually exists), Charles Darwin referred to earthworms as 'nature's ploughs' because of their role in mixing organic matter from dead organisms into the soil. The circle of life is not kept spinning by lions, no matter what Disney would have you believe. It's all about the earthworms.
Some of the best-known soil architects are the mound-building termites of Africa, Australia and South America. These termites aren't so different from all the other termites of the world, except that they adorn their underground nests with elaborate, aboveground mounds, constructed entirely from soil.
The mounds contain a dense network of tunnels and conduits whose main purpose is to provide ventilation for the nest underneath. The tunnels are usually built by the working caste: sexually immature termites who are blind and wingless. As their name suggests, they're the workers. They don't protect the nest from invaders or predators (that's the soldiers) and they don't get to have sex (that's the reproductive caste). They may not have much fun, but they are responsible for the magnificent mounds, some of which can reach more than thirty metres in diameter.
And the mounds aren't just visually striking; they also contribute to maintaining the diversity of surrounding plant life. In Africa, clusters of mounds belonging to Macrotermes termites allow for tree islands to grow in the middle of grassy oceans. It's thought this is in part because the termites, like earthworms, help dead plants to decompose and stir the organic matter into the soil. That makes the soil surrounding termite mounds more fertile than elsewhere.
You might think it's gross to pick up a dung beetle's dung ball, but that's only if you think it's made entirely of animal poop. And for some dung beetles, that's true. But the most impressive of dung balls are simply made of a small faeces-filled core surrounded by a mantle of plain old dirt.
After a male and female find a suitable bit of dung, the female lays her eggs in the middle of it. It provides not only a protective barrier for the developing beetle babies, but also a source of nutrition for the youngsters. In fact, most dung beetles continue to feed on dung throughout their lives (it being an excellent source not just of food but also of water). Once the eggs are safe inside the poop, the dung is then packed into a larger ball made of dirt. Then they get rolling. Typically it’s the male that does all the work, relying on the Milky Way or on moonlight to help him navigate, while the female just hangs on for the ride.
Most dung beetles can roll soil-packed dung balls that are up to ten times bigger than they are. Males of the species Onthophagus taurus are even more impressive: they can push balls up to 1,141 times their own body weight. To put that into perspective, that's like an average human pushing six double-decker buses. Full of people. (By comparison, the so-called 'World's Strongest Man' dragged a seventy-ton plane thirty meters in a bit less than a minute and a half. Which was only a paltry 411 times his own body weight.)
Think soil and you probably don't think parrots. But hundreds of brilliantly coloured macaws from around the Western Amazon basin flock each day (get it? you get it) to riverbanks where they dine on dirt. It's not just any dirt that attracts the birds, but clay, which is a catchall term for any fine-grained soil that contains minerals like iron or magnesium.
Careful observation by researchers in Peru has uncovered the reason for the riverbank parrot parties: they're after the salt. Salt is necessary for survival, but is really hard to find once you're more than one hundred kilometres from an ocean. So the parrots from all over the Western Amazon have learned to seek out the salt hiding in clay.
And the parrots aren't the only ones shovelling mouthfuls of soil into their gullets. The bats of the Amazonian rainforest do the same. But it turns out that they're not after the salt, like their avian counterparts. By keeping track of which species were visiting the clay licks, researchers in 2008 verified that fruit-eating bats were more likely to eat clay, despite the fact that it was the non-vegetarian (omnivorous) bats whose diets were more lacking in minerals.
Instead, they're after the detoxifying effects of the minerals found in the clay. Various toxins are found inside fruits, leaves and especially in seeds, and bats that gorge on those foods (especially pregnant and lactating females, who must provide not just for themselves but for their offspring) accumulate large doses of those toxins. It's those bats, carrying large doses of plant-based toxins, who find their way to clay licks more often. Because inside that clay is nature's medicine, a natural means for keeping the bats and their offspring safe.
Last but not least are the wolves. Unlike the worms and termites who live in soil, and unlike the beetles, parrots and bats, who eat soil, the wolves feature on this list because they eat moose. Wait, what? Keep reading.
It's all a part of the circle of life: moose eats plants, wolf eats moose. As the moose carcass decays, it briefly becomes host to temporary aggregations of microbes and fungi and other microscopic beasties feeding upon the death of the massive mammal. And those microbes and fungi help to provide nutrients for new plants. In 2009, researchers from Michigan Technological University turned to Isle Royale National Park, an island in the middle of Lake Superior, the largest of North America's Great Lakes. Because it's a well-studied island, the researchers had access to data from 50 years' worth of moose carcasses – more than 3,600 in total.
By now the story should be familiar. The decaying corpses allowed more nutrients to flow into the soil, making for more fertile soil, which could support more plants and a more diverse plant community. But it's not the moose who make this list, it's the wolves. That's because this version of the circle-of-life tale actually gets a bit more interesting.
It isn't just any old moose carcasses, but moose that were brought down by wolves that contributed the most to the soil. That's because the wolves' predatory behaviours influence where the moose hang out, which in turns influences the vegetation that relies on moose carcasses to thrive. Ungulate carcasses killed by carnivores also tend to decompose more completely than animals killed through other means, like starvation, disease, vehicle collisions and human hunting (which is not to say that those dead moose don't contribute to soil quality as well, just that they don't do it as comprehensively). "The connections we discovered are strong, yet unexpected," write the researchers, "because carnivores and soil [are] seemingly unrelated."
Top header image: Will Schrimshaw, Flickr