Worms: Gardener's Friend, Forests' Foe?

Written by Graelyn Brashear

If there’s any slimy creepy-crawler that people love despite its appearance, it’s the earthworm.

Most anyone will tell you that worms are gardeners’ friends, helpful creatures that break down dead leaves and other organic material and them it into rich soil. Even the U.S. Department of Agriculture has officially branded them beneficial.

It’s no wonder they’re well respected – they process plants into fertilizer at an astounding rate. As a result, worm-raising has taken off across the U.S. I even knew a girl who kept a bucket of worms in soil in her Philadelphia apartment, feeding them her kitchen scraps – a handy alternative to a garbage disposal.

But the real story of the earthworm and its relationship to our soil is far from simple.

What it is and what it does. Earthworms are segmented worms that burrow in dirt, munching through organic matter in order to digest the bacteria and fungi that proliferate on decaying plants.

There are, according to biologists, 182 species of the worms in North America. But here’s the thing: From New Jersey northward, every single squiggly earthworm is an exotic invader.

Any native worms living in the northern part of our continent were wiped out by the last ice age, which ended about 10,000 years ago. Great, hulking ice sheets up to two miles thick covered North America as far south as our great state of New Jersey, putting everything in a deep freeze and scraping the ground nearly free of life.

As a result, the native forests of the northeast we know today evolved in a wormless state, often in soil that’s relatively nutrient-poor. It took a long time for these woods to build up any level of organic matter, and the species that live there are dependent on slightly acidic, not-so-rich soil.

Enter the European colonists, who came to the New World on ships filled with soil ballast – and worms.

Over the last few centuries, worm populations have boomed in the temperate northern climates of the U.S., largely because of help from humans. Anglers toss their unused bait. Gardeners bring in big, beefy night crawlers from down south or overseas to enrich their soil.

And now, say biologists, worms have moved into our already shrinking woodlands and are changing the very chemistry of the soil, affecting the biology of deciduous forests from the ground up.

Why you should care

One size does not fit all when it comes to soil for plants. Oak trees and corn do not eat the same thing, so to speak.

Our introduced worm species specialize in tearing through leaf piles and transforming them into nitrogen-rich, alkaline soil – perfect for vegetable gardens, but essentially poisonous to our native woodland species.

What’s more, scientists say, worms are further disrupting the ecological balance of our woods by feasting on microbes that are vital to the health of plants and to the food chain of the forest. As a result, entire forests are sickening, and becoming much more vulnerable to invasive plant species. In our eyes, it might not seem like much is changing, but biologists say there’s been a big shift in the last few hundred years – in geologic time, a mere blip.

So what’s a forest-loving gardener to do? Technically, it’s illegal to kill worms because of their beneficial status. But you can help stop the spread by trying to keep them contained to your compost pile as much as possible, and avoiding bringing in more from worm farms. Don’t spread mulch or leaf litter near the edge of the woods, and if you use worms for fishing, don’t toss unused ones on the ground or in the water.

And if you're one of those soft-hearted folks that rescues stranded worms from sidewalks after rain? Maybe you should just let 'em squirm.