Natural Resources & Sustainability, Human Impact & Home

Earthworms: Champions of the Soil

By Peter Tonge

I'm returning to something I haven't done in more than a decade -- using earthworms to convert kitchen waste into the rich black soil amendment and fertilizer known as castings. I'm doing this to help out my daughter who lives next door.

For the most part I treat food waste the way nearly all gardeners do, by composting it. And that's what my daughter did until she ran into a little problem. Too much wet food relative to garden waste brought about a problem - a compost heap that the other week was alive with maggots.

Composting has become a very popular and very ecologically beneficial activity in many communities around the world. A great variety of things from home can be used for composting such as food wastes (pictured in the closed bin, left), grass, weeds and other wastes, as well as wood chips, hay and manure. The use of earthworms, as pictured in the open compost bend on the right, help ensure healthy composting. (Photos: Dromore National School - Ireland, left; Mansfield Middle School, Storrs, CT, right.)

Now maggots do a splendid job converting rotting food into rich plant nutrients, but they do so at a cost - flies. On the other hand, earthworms, those champions among food converters, never turn into anything other than more earthworms - lots of them. In fact, under ideal conditions, 10 pounds of redworms, sometimes called manure worms, can become two tons of the little wrigglers in just two years. That's why people who go in for earthworms seldom need to buy more, once the initial investment in breeding stock is made.

Soil Dwellers & Composters: An Ancient History

Redworms are also known as red wigglers, tiger worms and manure worms, among others. They are excellent for use in composting. (Photo: Vermitechnology Unlimited)

From the gardener's viewpoint, the many species of earthworms can be divided into two categories: soil dwellers -- often called nightcrawlers -- that consume both soil and organic matter, and redworms that live and thrive in almost pure organic matter, like manure piles for instance. The former you want in your garden beds, the latter in your compost piles or worm bins for the purpose of consuming food and other organic waste.

For three millennia (3,000 years), the thriving civilization of ancient Egypt was strikingly successful for two reasons: 1) The Nile River, which brought abundant water to the otherwise parched lands of the region; and 2) the billions of earthworms that converted the annual deposit of silt and organic matter, brought down by the annual floods into the richest food-producing soil anywhere. Those Egyptian worms are thought to be the founding stock of the nighcrawlers that slowly spread throughout Europe and eventually came to the Western Hemisphere with the early settlers.

Like the settlers, the European earthworms also thrived and, according to the USDA, an acre of good farm soil in North America is now populated by an average of 50,000 earthworms. But in soils rich in organic matter, populations can be considerably higher. The Good Gardeners Association in Britain, which follows a no-till, heavy composting policy, estimates earthworm populations can approach 3 million to the acre.

How Earthworms Work and Cleanse the Soil

Nightcrawlers are the most common type of worm found in your lawn and garden. They are not very useful for composting but they are extremely beneficial for the soil.

But what exactly do earthworms do? To start with they can rightly be considered tillers of the soil. As it tunnels through the soil, the active earthworm can eat between half and all of its own weight in soil and organic matter every 24 hours. In the process it excretes a super rich plant food, principally on the surface of the soil each night. According to USDA studies, those castings contain five times the nitrate, seven times the available phosphorous, three times the exchangeable magnesium, 11 times the potash and 1-1/2 times the calcium of the best top soil in the United States.

Compost is basically the decomposed remains of plants and other organic compounds (once-living materials) which have formed a dark, earthy substance full of nutrients and other soil-enriching compounds. (EPA Photo)

Earthworms are also great incubators for beneficial microorganisms (organisms of microscopic or ultramicroscopic size) as they travel through the earthworm, which some people describe as "one long intestine," Others, with a more scientific bent, refer to it as a "tubular bioreactor." In any event actinomycetes -- which give moist soil its pleasingly earthy smell, and bacteria can reach densities some 1,000 times greater than in the surrounding soil. At the same time, studies show pathogens (any substance that causes a disease), including salmonella and E. coli, are destroyed in the same journey through the earthworm gut. Competition from beneficial microorganisms is one reason. The oxygen-rich micro-environment created by the earthworm is also intolerable to human pathogens which are, for the most part, anaerobic.

Improving the Soil

Earthworms help create soil that roots can easily penetrate, resulting in healthier growth. (Pennsylvania Environmental Protection)

Of equal value to gardens is the remarkable tunneling done by earthworms. In moderate temperatures (65 to 75 degrees F.), earthworms work primarily in the top 10 to 12 inches of soil. Heat or cold, however, will drive them to depths as great as 6 feet.

These tunnels aerate the soil and also improve drainage. Roots have been found to travel down worm holes in their search for water and nutrients. Also, since earthworms have the habit of pulling leaf litter and other organic matter on the surface deep into their burrows, they effectively improve soil structure by boosting humus levels. When they die, earthworms which are 60 percent protein, add rich quantities of nitrogen to the soil. Little wonder Charles Darwin said in 1881: "It may be doubted whether there are many other creatures which have played so important a part in the history of the world."

USDA research many years ago documented the beneficial affects of earthworm castings when fed to potted plants. Researchers also noted improved plant growth when just a few dead earthworms were added to the soil in the pots.

Earthworms, it seems, are wanted, "dead or alive."

Did You Know?

• The U.S. Environmental Protection Agency estimates human refuse is composed of 14.6% yard waste, 6.7% food, and 7% wood. If these materials were used for composting instead, well over a quarter of our landfill requirements would be reduced.

• The nightcrawler is an example of where the introduction of a foreign species has been beneficial to the local ecology. The modern North American earthworm found its way from Europe in potted plants. Most of the native North American earthworms died during the last Ice Age which started about 70,000 years ago and lasted for about 60,000 years.

• The general lifespan of the earthworm, depending on the species, averages 4-8 years.

• The are up to 3,000 species of earthworms.

• In just one acre of land, there can be as many as a million earthworms!

• Earthworms can be as short as one-twenty-fifth (1/25th) of an inch and as long as 11 feet!

• Earthworms have a lot of heart, so to speak! Some species have as many as 10 hearts!

• And how do they breathe so far underground? Since earthworms don't have lungs, they breathe through their skin. By improving the soil by breaking it up and aerating it, these worms are also creating a healthy environment for themselves.