All About Earthworms

Earthworms are good for plenty more than improving soil quality and baiting the old fishing hook.

Worm composter

In the compost pile and then in the garden, earthworms are nature's compost engineers.

Photo by Kevin Fogle

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Picture it: You’re wrist-deep in loose soil when you feel something slide across the back of your hand. Eeeuwww. Your knee-jerk reaction might be to yank yourself back from the soil – your skin isn’t the only thing that’s crawling.

Pity the first person who noticed an earthworm at his or her feet. He surely jumped in fright – the creature looked like a snake, only smaller. It wiggled like a snake, only sort of. Birds and rats ate them raw, but it was no gustatory treat. She must’ve wondered how it got there, but today’s scientists aren’t even sure: Because earthworms’ soft bodies aren’t conducive to leaving fossils, there’s just no way of knowing. Oligochaetologists – specialists who study worms – theorize that earthworms came ashore well after the formation of soil, perhaps around 350 million years ago, give or take a few months.

Even so, there was a time when big swaths of North America were wormless. Thousands of years ago, glaciers scraped the soil away from the continent’s northern parts and either moved or killed the earthworms. That means, assuming you don’t live in a desert or on another glacier – places where earthworms don’t care much for the real estate – the ancestors of the crawlers in your backyard got there by hitching a ride, probably from Europe.

Though there are more than 6,000 named species of earthworms, they fall under three basic categories, according to where they live. Epigeic worms are commonly found in rotting material, like those red wigglers in your compost heap; endogeic worms live in topsoil and almost never come above ground; and anecic worms are the ones that dig deep into the soil – known to most of us as nightcrawlers. The former two worm types don’t live very long – sometimes just a few weeks. The latter enjoys a nice long life and Sundays with his grandkids.

Every child worth his salt has heard that earthworms have the ability to regenerate if they’re cut in half. In truth, some worms can regenerate, depending on where they’re cut, and some will grow new tails multiple times. Others will simply die in two pieces. At any rate, worms never regenerate more segments than were removed. By the way, the jury’s still out on whether or not this method of doubling your worm herd causes pain to the worm, but you probably needn’t worry about any kind of head count – there could be more than a million earthworms per acre in your soil, if it’s healthy. Just one of those little guys could digest 36 tons of soil this year.

Now that you’re getting up-close and personal with an earthworm, you’ll notice that they’re pretty interesting individuals. With no eyes, earthworms can’t see, yet they are sensitive to light. With no ears, they can’t hear, but they can sense vibrations in the soil. They don’t have lungs, but they breathe through their skin. They have between one and five pairs of hearts, and both male and female sexual organs. Because of their teensy and very primitive brains, you can forget about finding a Worm Einstein, but that’s OK, because worms know how to do something a whole lot better.

Using their setae – tiny bristles that cover each segment – worms work their way through the soil, moving a few inches a day and eating about a third of their bodyweight in dirt, rotting vegetable matter, bacteria and fungi. While doing this, they redistribute nutrients beneath the ground through movement and their excreta – called casts, which, incidentally, have absolutely nothing to do with Broadway or broken arms. This changes the construction of the soil, not only by aerating it, but also by killing harmful bacteria, increasing water flow, utilizing dead material, and loosening the soil to allow plant roots to grow.

And that’s just what worms do in your garden. They also help archaeologists by burying ancient artifacts with new soil. In some areas, they serve as food and are used in traditional medicines. They also feed songbirds and make mighty fine fishing companions.

Though there are exceptions – nightcrawlers, for instance, can ruin the regrowth of forests, and worms can ruin rice paddies – earthworms are pretty well essential for the existence of human life because of what they do and how they benefit plants. So the next time you go to bait that hook and try to catch dinner, just think of the multitude of ways that earthworms aid our food production!


Terri Schlichenmeyer, book reviewer and trivia collector, lives in Wisconsin with her two dogs and more than 11,000 books.