Rare is the soil without earthworms.
Good thing, too, because they play a huge role in keeping soil healthy and fertile.
“They’re humongous vacuum tubes and they inoculate things along the way,” said Jill Clapperton, the North American expert on earthworms.
The founder of Worm Watch, Canada’s ecological monitoring and assessment program, and a former Agriculture Canada rhizosphere ecologist, Clapperton now operates a consulting company in Montana where she spends a lot of time working on “soil animals.”
Read Also
Alberta crop diversification centres receive funding
$5.2 million of provincial funding pumped into crop diversity research centres
She calls earthworms ecosystem engineers because they have such an effect on soil structure and ecosystem function. That effect is visible, unlike those of other organisms in the soil.
“Their tunnels have a dramatic effect on aeration and water infiltration and also on the earthworms themselves,” Clapperton said.
“When they are moving through the soil, they breathe and they excrete through their skins as well, so the slime that is on their bodies, that’s protecting their bodies and lubricating their bodies, is actually a very rich carbohydrate source as well as a calcium source.”
The tunnels form what she calls a drilosphere.
Plant roots move easily through the drilosphere and prefer to do so because the tunnel walls are lined with protective rhizobacteria.
Clapperton said earthworms and other soil fauna are often overlooked in terms of their important role in soil structure.
Protozoa and nematodes, which eat bacteria and fungi, require the earthworm tunnels to move through the soil. The plant roots create currents in the tunnels and pull the small organisms along as they pull up water.
Soil with a continuous tunnel network would have a lattice-like structure if a cross-section were examined, she said.
“It really looks all puffed up, like bread after it’s risen.… It has a really nice structure. It’s fairly light, not really heavy. It absorbs a lot of water and maintains its structure and doesn’t collapse.”
Within that structure, slightly smaller organisms such as mites and Collembola, or springtails, work in the decomposition layer near the soil surface. They chew up the material between the veins of leaves, for example, leaving the woody parts to fungi.
Terry Tollefson, associate professor of soil science at the University of Saskatchewan, calls these organisms the early preparers.
“They hasten the decomposition of organic matter through their coarser feeding activity,” he said.
“This makes the organic material smaller and facilitates the more active ultimate decomposition by the micro part of the group.”
The earthworms and enchytraeids, or pot worms, work throughout the soil layers.
“They work in the litter layer pulling things down and working around in there, and then they also work deeper down in the soil, so they’re recycling, and that’s why Darwin called them nature’s plow,” Clapperton said.
Pot worms are smaller, look exactly like earthworms and are considered excellent indicators of soil quality.
They are found in some of the grey, wooded soils where there are few earthworms.
These are the tiny earthworms that curl up immediately when exposed.
“In Europe, they actually consider these a better indicator of soil quality than earthworms themselves because they actually probably mineralize more nitrogen for their body mass than do earthworms,” she said.
Most people think all earthworms are the same, but there are species that live in different layers of the soil and do different jobs. Some live in the upper layers and work with the mites to incorporate litter.
Others spend time at both the surface and in the deep layers.
Their activity creates more microbial activity because they create little sites where they leave their waste and organic matter.
“At the same time, they’re creating all these wonderful big tunnels,” Clapperton said.
Some earthworms will burrow two to three metres, or as deep as the soil goes.
Night crawlers, which are the large, deep vertical burrowers, live only in their own tunnels and move up and down.
Other soil animals include ants and termites, which, while people consider them pests, also create structure.
There is a smaller, different role for insect larvae found in the soil. For example, wireworms are actually the larvae of the click beetle. A large population of wireworms indicates a heavy infestation of the beetles.
“It means that we’re putting a lot of food in a habitat for click beetles,” Clapperton said. “That probably means that our integrated pest management is off kilter and we need to adjust it.”
In terms of chemical pest management, some fungicides will kill earthworms, and insecticides can be toxic to them and other critters as well.
“A lot of time we rely on insect larvae and insect-related organisms to break down surface residues,” she said.
“We don’t have the same number of organisms capable of feeding on that because it’s toxic to them.”
Tillage has more of an effect on microorganisms but does destroy the soil structure that earthworms have worked so hard to create.
Tollefson said less tillage likely means more earthworms, although that hasn’t been studied.
“The return of the earthworm is an indication of better soil health,” he said. “In a fertile soil, what we expect to see is a huge diversity of organisms.
“It is often said that a teaspoon of surface soil from a very good or very active or productive soil will contain more species than exist above the soil.”
True or false: If you cut an earthworm in half, both parts will regenerate and you will have two worms.
False. You will end up with a dead worm or a shorter worm and half a worm carcass, which will quickly decompose. The head region is the most important part of a worm and if it remains intact, the worm can potentially survive. It may grow a new tail, which may be stubby in appearance. The lower fragment will simply die.
