The Dirt on Earthworms

By Tina Patterson

Like Rodney Dangerfield, the lowly earthworm gets no respect. Yet, this seemingly unimportant lumbricid is an indicator of soil health, and can dramatically impact soil structure, water movement, nutrient dynamics and plant growth. There are 21 different species of earthworms in Michigan, and 50-300 worms can be found in a square yard of cropland nutrient-rich soil.

Earthworms are made up of many small segments, each segment with many small hairs that assist the worm in movement, aided by a slimy mucus that it produces. Without a skeletal system, the worm is heavily muscled. The blood circulating through its system gives it a reddish color. Earthworms can live up to eight years, but most do not survive more than a year.

Moist soils are necessary for earthworms to thrive, and the majority of worms are found in the top meter of soil, most often just below the surface where there is plenty of decomposing plant material. Earthworms consume dead and decaying plant material and are prey to robins, red-winged blackbirds, crows and other ground-feeding birds as well as foxes, shrews, skunks, moles and garter snakes. During droughts or winter freeze, earthworms may go deeper than the top meter of soil. Worm tunnels have been found at depths of 16 feet.

Earthworms promote a healthy environment in the following ways:

• Worms eat microorganisms and produce organic matter in their feces or casts that becomes plant food.

• Casts help move large amounts of soil to the surface and carry organic matter to the lower strata.

• Earthworms help with soil drainage, acting as a conduit for rain, especially after a heavy downpour. These burrows minimize soil erosion and increase porosity and drainage.

• By fragmenting organic matter and increasing soil porosity, earthworms increase soil water retention ability.

• Channels made by earthworms are rich in nutrients and provide space for root growth. This makes it easier for plants to set a deep root base.

• As earthworms eat the plant and crop residue, the castings they leave behind provide nutrients to the upper soil levels and the surface residue is pulled into their burrows.

Earthworms are more than good fish bait; they play an integral part in keeping soil rich with nutrients and maintaining a healthy environment for farms, fields and forests. So the next time you see a worm crawling on the sidewalk after a heavy rain, give it some respect.