The giant Palouse earthworm lives! The worm many thought as the stuff of legends or myth was found alive earlier this year by some researchers from the University of Idaho. While its discovery was an intriguing note of science, ordinary earthworms we encounter in the garden every day are no less noteworthy.
Earthworms are nature’s most powerful ally in creating soil texture as they search the top layers of soil for a meal of compost, fungi or other organic material. The digested remains of their meals become food for other soil microbes and nutrients for plants. As they eat they mix and loosen soil particles so air and water can get into the soil. By one research estimate worms can process 16,000 pounds of soil per acre per year; 30,000 pounds if there are lots of them.
For all their power in moving soil, earthworms are very simple creatures. Their long, thin bodies are perfect for going through narrow tube tunnels aided by a simple brain that controls little more than the contraction and elongation of different sets of muscles to move them through the soil.
Worms “see” through a series of light-sensitive cells in their skin. When they are hit with light, the cells tell them to head underground quick so they don’t dry out on the surface. This is why they wiggle so wildly when we turn them up in the dirt. They breathe by infusing oxygen directly through their skin from air or water.
Our Inland Northwest gardens are home to three major types of worms. Night crawlers, the largest at eight to ten inches, dig deep vertical burrows between the subsoil and the surface of the ground. They come to the surface at night and pull organic matter back into their burrows and often leave a little pile of castings at the top of their burrow to seal it. These worms are common in moist areas under trees, where the soil is not regularly tilled.
Our most common worms are garden and manure worms that can get five to seven inches long and live in the top foot or so of soil. They are most active in the spring and fall when the soil is comfortably warm. In the winter and the hottest part of the summer, they retreat deeper into the ground and go into hibernation. In the winter, they will actually freeze in the soil.
Red wigglers are common in compost piles and are only about three to four inches in length. These are the easiest worms to raise in captivity and are what you get when you buy worms for a compost pile or a worm box.
To encourage earthworks in your garden, add lots of organic matter to the soil. Keep mechanical rototilling to a minimum to reduce the damage to their tunnels and outright death by the chopping blades of the machine. Contrary to some beliefs, cutting a worm in half does not make two worms; it kills it.
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