The mighty worm

Look out the window. See a patch of earth? How many worms do you think live there? Every acre is home to as many as 1 million worms. This means that for every square foot (12 inches by 12 inches), there could be 23 earthworms.

Fossil evidence shows that wormlike creatures have been around for more than half a billion years. They existed in the time of dinosaurs and even survived the mass extinction 65 million years ago - the one that finished off the dinosaurs. Earthworms typically live anywhere that's not extremely hot or extremely cold.

Glaciers are extremely cold. They also act like giant bulldozers, scraping off the top layer of soil. So by the end of the last Ice Age in North America (about 10,000 years ago), earthworms in what is now Canada and the US had been wiped out. Most of the earthworms found today in North America are immigrants. They came here in potted plants and ship ballasts from Europe. We're glad worms have found good homes here, for the most part.

As settlers moved West, worms moved with them. Worm eggs were carried on the soles of dirty shoes and in horses' hooves. They hitched rides on wagon wheels and, again, in pots. The worms arrived in California with the Forty- Niners during the Gold Rush. In all, it took only 200 years for earthworms to make their homes all across America.

Earthworms eat their way through soil. They ingest bacteria and small particles and enrich the earth with their waste products, called castings. The burrowing action also allows more water and air to enter the soil, making it richer. This deceptively simple creature is largely responsible for all the rich soil on Earth. Its journey across America has created some of the richest farmland in the world.

Nineteenth-century British scientist Charles Darwin, who wrote "The Origin of Species" about evolution in 1859, studied worms. He wrote a whole book about worms called "The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habitats" in 1881. ("Vegetable mould" is what soil used to be called.)

Darwin called worms "ploughs of the earth" because of their ability to eat soil and eject it as castings. He believed that worm castings and the movement of worms were wholly responsible for the top layer of rich soil. Darwin claimed that worms were one of the most important creatures in the ecosystem. He also noted the amazing ability of worms to bury things in the soil - from coins to Roman ruins. Archaeologists should be very grateful for worms!

The worms in your garden are probably nightcrawlers. They pull organic material - leaves, remains of plants and animals - into their burrows. The best time to look for worms is at night. Worms are sensitive to light and dig away from it.

Red wigglers are another common worm, though probably not in your yard. They do not make burrows. They feed on the surface of the soil, eating organic material that has started to decompose. Red wigglers are popular with farmers and gardeners. Their diet also makes them perfect for composting kitchen scraps into rich soil. They are commonly used in worm composters. (These are special boxes with trays and lids where worms digest household scraps - except for meat and dairy waste.)

Red wigglers eat half their body weight in food every day. Matt Abbruscato, owner of Foothill Worm Farm in Pleasanton, Calif., does the math: "One pound of red worms eats one-half pound of food per day. Thirty-two pounds of worms eat 16 pounds of food waste a day." That's what he needs to feed his 30 bins of worms. That's a lot of waste not going to a landfill.

Mr. Abbruscato sells worm castings, red wigglers, and a fertilizer he calls "worm tea," made from worm castings. The "tea bag" is a large lump of castings in a cheesecloth sack. It is steeped in water to create a strong infusion that is poured over plants.

"Castings provide a really good defense against pests," he says.

Abbruscato sells mainly to private customers and to schools running composting projects. Customers love the effects of the castings and worm tea. Roses grow bigger. Vegetables taste better. Abbruscato says this is because chemical fertilizer makes food taste blander.

Every three or four months, Abbruscato's worm population doubles. But worms hibernate in winter. Eggs won't hatch until the soil is 55 to 60 degrees F, he says. The eggs look like little white pearls in the soil. When they hatch, they leave a brown shell behind.

Abbruscato loves to experiment with the worms' food choices. They definitely have preferences, he says. "They will eat any organic material," he says. That includes cotton jeans, shirts, and even "my wife's old nightgown. They went through that in about four days."

He holds up what's left of a pair of jeans - just the Levi's tag and the zipper. The worms like to eat the bacteria and decomposing material. "With the jeans, they are eating the bacteria that eats the jeans," Abbruscato says. When they eat the bacteria, they end up eating the jeans, too.

In some places, however, worms are seen as a problem. Forests from Minnesota to Rhode Island are battling a worm invasion. Worm-free since the Ice Ages, these remote forests have been getting on just fine without worms.

With the arrival of worms in the past few decades, some forest floors have been cleared. The worms have eaten all the leaves and decomposing vegetation underneath them called "duff." Many seeds germinate in the duff. Without it, some seeds won't grow, and some animals lose their habitat. Water runs off the empty forest floor quickly, changing the drainage of the forest. The humble worm is changing the ecosystem, wiping out some native plant species.

This sudden invasion could have happened only with human help. The offending worms are probably the offspring of fishing bait discarded at the end of the day.

Scientists are working on ways to regenerate these forests. Car tires can transport worm eggs, so road building is being halted in sensitive areas. Native plants are being grown and replanted in the forests.

We are finally realizing just how mighty the humble earthworm can be.

Most earthworms are a few inches long, but some of the world's biggest worms can grow up to 22 feet - longer than an SUV! Here are several examples:

United States

The Oregon Worm grows two to three feet long, and it gives off the smell of lilies when handled. It burrows five feet deep and is rarely seen. In fact, there have been no official sightings since the 1980s.

The Giant Palouse was found in Washington State. It grows up to two feet long - about the length of a baseball bat. It hasn't been spotted since 1978. Population growth and development may be to blame.

Australia

The Giant Gippsland can grow to three feet, but it can stretch up to 10 feet. It's rarely seen, but Australian farmers can hear gurgling sounds coming from the ground as it moves through the earth.

New Zealand

The North Auckland Worm grows 4-1/2 feet long and gives off light at night. It's so bright you can read by its light.

South Africa

The South African Giant Earthworm grows to be up to 22 feet and is the largest earthworm known. The record-setting specimen was found beside a road in William's Town, South Africa, in 1967. The worms normally grow to only about six feet. (Did I say "only"?)

• Some earthworms can survive two miles below the surface, where temperatures can reach 160 degrees F.

• Some worms can digest pollution. Scientists are figuring out if the worms could be used as toxic-soil detectors, the way canaries were used as poisonous-air detectors in mines.

• The slime or mucus made by an earthworm helps to keep its skin moist so it can breathe. It also helps it move smoothly through its burrow.

• A snakelike indigo-blue worm with white and yellow markings lives in the Philippines. It crawls on the forest floor.

• Earthworms are nature's power bars. They make a great snack for animals and are a key part of the food chain.