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Invasion of the Killer Worms

Commonly viewed as beneficial, the creatures are slowly destroying the ecosystem in many North American forests, where they're not native.

September 18, 2003|Eric Slater | Times Staff Writer

DULUTH, Minn. — The bluebead lily and red bainberry plants were few, the forest floor nearly denuded and still. When the solution of pulverized mustard seed and water seeped in, though, the ground began to churn.

Up came the worms, wriggling and writhing, Lumbricus terrestris and Luumbricus rubellus frantically trying to evade the homemade skin irritant only to find themselves in the clutches of Cindy Hale, and science.

The worms, it seems, those hermaphroditic wonders of expeditious composting and ecologically friendly farming, are responsible for the paucity of native plants and creatures on this hillside in Tettegouche State Park. While good for many things, earthworms appear to be stripping some North American forests of their most essential feature: the decomposing leaves and other forest litter called duff, which provides nutrients and sanctuary to new generations of trees, plants and animals.

"There's this mythology that worms are benevolent creatures who aerate the soil for human benefit," said Hale, a doctoral student at the University of Minnesota, as she knelt recently in the dirt, a Lumbricus terrestris, or night crawler, twisting in her fingers. "Well, sometimes we like what worms do, but we certainly don't like what they do in our forests."

For The Record
Los Angeles Times Saturday September 20, 2003 Home Edition Main News Part A Page 2 National Desk 2 inches; 76 words Type of Material: Correction
Earthworms -- In Thursday's Section A story about invasive worms in North American forests, the name of a plant, red baneberry, was misspelled as red bainberry. One reference to the Latin word Lumbricus was misspelled Luumbricus. A paragraph about redback salamanders said they are "the most abundant creatures in many Eastern forests." Insects and some small invertebrates outnumber the salamanders, but salamanders account for the most mass of any creature in the forests, according to scientists.

In much of North America, worms are not the ancient natives many people assume. They are exotic and relatively recent invaders.

North of a line that stretches from Washington state to New York, with a dip below the Great Lakes, native earthworms vanished about 10,000 years ago, scientists believe, swept away by the receding glaciers of the last Ice Age.

The first nonnative worms were brought to the region by early explorers, in the soil-ballast of their ships, the manure of their horses. Others were loosed in forests more recently by woodland homeowners planting greenery whose potted soil contained worms and, perhaps most dramatically, by fishermen dumping their bait at the end of the day.

"There's Mic Mac lodge," Hale said, pointing to a collection of huts dating from the 1950s. "The leading edge of the invasion runs right through here."

Now a small campsite, Mic Mac was once a fishing lodge on the shores of the small canoe haven of Lake Mic Mac. It is also the epicenter, scientists believe, of one worm invasion that now spreads out for nearly half a mile in every direction.

Inside the area occupied by worms, yellow birch, white spruce and oak trees still stand tall, but few smaller plants remain in what scientists call the understory, and the duff is all but gone. Beyond the worms' front line, the duff is thick and soft, the thimbleberry shrubs, spurred gentian flowers and dozens of other plants so dense they tangle in your bootlaces.

Praise for the Worms

Although oligochaetologist Gordon Gates first suggested in the 1960s that nonnative worms were invading forests, praise for earthworms has long outpaced scientific study of their effects on forests -- and understandably so.

Since 1881, when no less a scientific mind than Charles Darwin demonstrated that the worms in an acre of soil could produce 18 tons of nutrient-rich castings annually merely by passing vegetation through their guts, earthworms have been hailed as masters of beneficial decay and aeration.

Little more than tubes of digestive tract, many sporting both male and female reproductive organs, earthworms have seen their beneficent reputation grow even larger in recent decades as environmentally conscious farming and composting have become popular.

Two pounds of Lumbricus rubellus, or redworms -- another nonnative species now found in forests -- can gobble their way through one pound of kitchen waste in a day. Most worms consume about 10 times their bodyweight each month and at the same time act as biological rototillers, aerating and turning over soil.

If their brains weren't the size of a pinpoint, worms might indeed enjoy the celebrity that has made them a multimillion-dollar business, with Canada, the largest exporter, alone doing $20 million in sales a year, most sent to the United States.

A worm broker in Scotland ships them first-class in "Handy-sized fish bait pots with sealed lids." Another in New Zealand offers a mix of 4,000 composting worms for the sale price of $45.50. And a New Jersey worm rancher offers tips on mailing worms during the holiday season.

Gardeners, 4-H clubs and hundreds of schools and universities are among those who buy worms to help in gardening and composting. This is all very well, scientists say, so long as buyers keep a handle on their wrigglers; the very traits that make them perfect for composting and aerating also mean they are voracious plows in the forest.

Following the Ice Age, forests evolved -- sans worms -- into ecosystems that exchange nutrients slowly. Worms operate in the opposite manner, eating and returning nutrients to the soil through castings very quickly.

Quick Work

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