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Sunday, 14 January 2007

Down & Dirty

September 19, 2006

The Columbus Dispatch

By Mike Lafferty


Earthworms quietly alter the world's soil a mouthful at a time

Charles Darwin's theory of evolution came about in part because he noticed the little things.

He filled volumes of notebooks with his exacting observations of everything from birds to barnacles during his five-year voyage aboard the HMS Beagle.

Most famously, he recorded the differences in beaks of finches that live on the various Galapagos Islands.

When he returned to England, Darwin continued his search for evidence to support his budding theory, and studied the plants and animals around Down House, his country estate.

Eventually, Darwin turned his attention to earthworms, animals that most naturalists of the day ignored.

In what is considered a classic natural-history experiment, Darwin observed the way earthworms dragged twigs into their burrows.

He showed that rather than randomly grasping twigs, worms gather them at their narrow ends so that they can easily be hauled through a burrow entrance.

"It almost seems like intelligence," said Clive Edwards, an Ohio State University biologist who many times has duplicated the experiment.

Darwin spent nearly four decades observing earthworms, recording their behavior, measuring the amount of soil they move, evaluating their influence on soil fertility.

In 1881, he published The Formation of Vegetable Mould Through the Action of Worms with Observations on their Habits.

" ... it may be doubted if there are any other animals which have played such an important part in the history of the world as these lowly organized creatures," he wrote.

And new research, including some by Edwards, shows that not all of it is good. Even the earthworm can wreak a bit of havoc among ecosystems.

There are more than 5,500 known species of earthworms living on the planet in all but the hottest and the coldest zones. They range in size from less than an inch to more than 10 feet long.

Aristotle called them the intestines of Earth. By Victorian times, they were popularly associated with disease because they often were found in rotting vegetation.

Darwin, however, elevated earthworms. His observations revealed the dramatic effect they have on soil.

Toiling out of sight, they are indeed miniature plows, tunneling passageways that carry air and water deep underground.

Darwin calculated that over a decade, the worms on an acre of soil could create a layer of nutrient-rich droppings, known as castings, about 2 inches thick.

Modern studies confirm Darwin's ideas.

"A good agricultural population of earthworms will turn over the top 6 inches of soil every 20 years," Edwards said.

New Zealand scientists reported earlier this year that the total weight of earthworms in a farm pasture can exceed the weight of animals grazing there.

Edwards, who has studied earthworms nearly as long as Darwin did, is the go-to worm guy these days.

Since 1990 he has been awarded more than $4 million in federal grants to study earthworms. He's working on the fourth edition of his book, Biology and Ecology of Earthworms, and recently returned from Poland, where he gave a presentation at the eighth International Symposium on Earthworm Ecology.

And, like Darwin, he is one of their greatest boosters, citing their effect on soil. Others are joining in the praise.

"The most fertile fields in the world are chock full of earthworms. They aerate and improve soil structure," said Patrick Bohlen, a scientist at the Archbold Biological Station, a privately funded agricultural-science lab in Lake Placid, Fla.

And in these ecologically conscious days, earthworms are big business.

In Cleveland, where steel and shipping used to drive the economy, earthworms are becoming a money-maker.

By April 2007, what is being billed as the largest indoor earthworm-composting facility in the world is scheduled to open in a former auto-parts plant.  It has been said the company doing this can actually assist in turning around Cleveland's distressed economy.

Resources in, Castings out.

"Once we get going, we will process organic recoverable resources every day," said an informative and candid Jamie Melvin, President of Sansai Environmental Technologies.

"They eat anything that's not rubber, glass, metal or plastic."

Melvin said the operation's red wiggler earthworms will transform post consumer materials from hotels and restaurants into tons of earthworm compost, called vermicompost, each day for sale to a variety of vendors.

Red wigglers also are the most common home-composting worms. They can survive in organic materials and turn kitchen scraps into a soil amendment.

But some new research by Edwards and colleagues at Ohio State indicates a dark side to earthworms.

For example, studies suggest that earthworms seem to like ragweed, and pull the plant's seeds into the soil.

"Here we have earthworms promoting weed growth," Edwards said. "They pick up the seeds -- it's difficult to believe they do it -- and drag them into their burrows.

"It's the first example of an earthworm having a major impact on an important weed."

And some scientists blame earthworms for pushing the decline of some northern forests.

"Some of these forests have thick organic layer built up over hundreds of years," Bohlen said. "When earthworms invade, they completely eliminate that layer."

Earthworms mix organic matter into the soil and make it easier for bacteria and other soil microorganisms to break it down. And stripping that organic layer exposes tree roots and can cause soil erosion.

This drives out plants such as trout lily and native ferns, opening the forest floor for weedy foreign invaders such as garlic mustard and Japanese barberry.

The most familiar earthworms, including those in Ohio, are foreign, mostly from Europe.

Settlers bought them when they arrived and began building cabins, plowing fields and planting crops along waterways such as the Great Miami, Scioto and Muskingum rivers.

The worms, especially the night crawler from the family Lumbridicidae, spread from there.

Ohio was virgin territory for these invaders. The last glacier wiped out most worms in the northern hemisphere when it moved south from the Arctic 50,000 years ago. When the ice retreated 12,000 to 14,000 years ago, worms were slow to return.

Native worms are still relatively plentiful in Kentucky, where the glaciers did not reach. And Bohlen said he has found native worms in Ohio, but only in isolated places such as marshes or in rotting logs in oldgrowth forests in the state. European worms have higher reproductive rates and can quickly overwhelm native competition. They also are highly adapted to moving with people on farm trucks, tractor tires or in garden-center plants.

Their harsh effect on Minnesota woodlands prompted officials there to launch an information campaign urging fishermen not to throw away their unused earthworms.

They're not invincible. Worms are highly sensitive to pesticides, especially fungicides.

Biologists restored Penn Forest, near Philadelphia, by adding sulfur pellets to the soil, dramatically lowering soil acidity and killing off the earthworms.

Bohlen said it is possible to restore small forests this way.

But with fears that carbon dioxide from burning fossil fuels is boosting global warming, humans might want to promote worms.

Preliminary research at the University of California showed that earthworms help stabilize carbon in the soil by boosting the soil's ability to sequester carbon. They do this by helping carbon bind to soil minerals, making it less likely microorganisms can free it to the atmosphere as carbon dioxide.

In another experiment, Swiss scientists have shown that boosting carbon-dioxide gas over grasslands created a synergy that stimulated earthworm growth and castings production. This, in turn, promoted the growth of grass, which tied up more carbon dioxide from reaching the atmosphere.

So the future might find humans depending on earthworms more than ever.

Darwin probably wouldn’t be surprised.

Last Updated ( Sunday, 14 January 2007 )
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