Counting earthworm populations may be the hip new thing for some, but Charles Darwin was doing it back in the 1800s, "before it was cool." The famous pioneer of natural selection and evolution spent plenty of time digging in the dirt and studying earthworms, and published his findings in 1881 in his book, The Formation of Vegetable Mould through the Action of Worms, with Observations of their Habits.
The relationship between soil health and earthworm populations is well-documented. These days, avid no-tillers and cover croppers often use earthworm populations as an indication of how healthy their soil is – and rightfully so.
Earthworms eat their way through the soil. The more food or residue that's left behind to feed the micro-herd below the surface, the greater their numbers are. As worms eat residue, they also eat soil and bacteria to break down the residue while passing it through their digestive systems. As they consume soil, they also move the soil.
In his studies, Darwin documented how earthworms gradually cover objects on the ground with their casts. Have you ever noticed a sidewalk or aging concrete foundation that appeared to be "sinking" in the ground? As early as the 1950s, studies have continually shown this soil movement by earthworms plays a role in the burial of artifacts. In 1957, British archeologist Richard J.C. Atkinson documented how contrary to popular belief, archeological sites and the soils beneath are not static, and earthworms, along with other forms of life beneath the surface, can change the soil and move objects deeper into the soil.
With enough food present, earthworms can turn over the top six inches of the soil in 10 to 20 years, according to NRCS. Meanwhile, their burrows improve water infiltration in the soil, and by spreading out organic matter and improving soil porosity, they improve water-holding capacity. These tunnels also serve as channels for root growth .As they consume residue and organic matter, earthworms also bury plant residue. After they consume soil and organic matter, they also excrete waste in the form of casts, a kind of soil aggregate. By doing this, they also carry organic matter deeper into the soil.
It's no wonder Darwin referred to them as, "nature's ploughs."