How Earthworms Discovered America

Columbus wasn't the only one on the move during the Age of Exploration.

You can't see them, but they’re there.

Image: MPI/Getty Images

Shortly after 1492, earthworms discovered America. Not in any heroic sense, of course -- but once those European worms arrived, they set to work reshaping the structure of American soil and devouring leaf litter that had been a source of food for countless insects, and the birds and mammals that fed on them. Creatures that had thrived died, and others took their place.

In his book “1493: Uncovering the New World Columbus Created,” Charles Mann quotes University of Minnesota biologist Cindy Hale on this turn of events: “Four centuries ago, we launched this gigantic unplanned ecological experiment,” she said. “We have no idea what the long-term consequences will be.” We’re still being surprised.

A great biological upheaval started with the voyage of Columbus, whose landing in the New World is celebrated in some quarters this weekend, as others have switched to observing Indigenous Peoples’ Day. Some who object to this change argue that it paves over history -- but there’s a big difference between the actual events of the past and the myths American schoolkids get taught. For example, Columbus (or Colón, in Spanish) was apparently slow to accept that the Earth was spherical. He had his own bizarre theory that was not scientifically viable. And the New World was no sparsely populated frontier: The best expert consensus, according to environmental historian John McNeill, is that between 40 million and 70 million people lived there.

The story of how European colonists inflicted a “gigantic unplanned ecological experiment” on North America has been similarly overlooked. “One of the great underappreciated truths about history is that the great majority of what happens is not the result of intentional action,” said McNeill. The unintended biological transfers that started with Columbus continue into this century. If anything, the pace has recently picked up, he said, along with the scope and pace of air travel and freight shipping.

But even early on, the world’s ecology was in shock. “Earthworms, mosquitoes, and cockroaches, honeybees, dandelions and African grasses, rats of every description -- all of them poured from the hulls of Colon’s vessels and those that followed,” wrote Mann. Ecological changes made many places unrecognizable to the people who had lived there for centuries.

Mann quotes biologist E.O. Wilson’s observation that Europeans unknowingly introduced a creature called a scale insect to Hispaniola -- the island of Columbus’s first settlement. Scale insects had no natural enemies in the Americas, so their population instantly boomed. The insects destroyed plantations, and, worse still, their wastes turned out to be delicious to fire ants. What the Spanish colonists noticed was that swarms of these stinging ants blackened their houses, inside and out, “as if they had been sprayed with charcoal dust.” Neighborhoods and communities were abandoned.

What happened after 1492 was not just an exchange between the Americas and Europe, but between the Americas and Africa and Asia as well. Southern plantations cultivated African rice, and Chinese farmers started to plant American corn to feed livestock, as well as peanuts and sweet potatoes.

And there were unintended consequences around the world, said McNeill. Potatoes, an American crop, grew well in many areas of Europe, especially Ireland -- leaving people there vulnerable when a blight destroyed crops. Similarly, in the early 1500s, American maize arrived in Africa. Not only did maize allow some populations to grow, it changed world history because it was storable and portable, said McNeill. Africans who had depended on more perishable yams and bananas as staples could only send armies on campaign for a few days before their food went bad. With maize, groups could send their armies far afield for weeks, allowing the growth of militarized states. And food that can be stored can be hoarded, allowing a more exploitative form of political power.

Some scholars have referred to our current period as the homogenocene -- a great mixing of species that had been evolving in separate directions for eons. Geography and history professor Alfred Crosby, whose work Mann cites as the foundation for “1493,” wrote that it was like reknitting the seams of the great supercontinent Pangaea, which has been broken apart for the last 150 million years.

Stanford University biologist Harold Mooney agrees that the unintended parts of the Columbus’s journey continue to reshape the planet. In his state of California, he said, native chaparral is disappearing, and mighty oaks are succumbing to a foreign fungus. Fire is a bigger danger because native plants are being replaced by fire-prone invaders from other parts of the globe. Many of the weeds that prompt the spraying of herbicides are in fact hardy, non-native species.

Historian McNeill said much of the credit for understanding the world this way goes to Crosby, who wrote “The Columbian Exchange: Biological and Cultural Consequences of 1492, published in 1972, and “Ecological Imperialism,” published in 1986. “The Columbian Exchange” was rejected by 40 publishers, said McNeill, a hurdle that Mann writes about in his book. McNeill said he thinks the reason was probably that they couldn’t fit it into a category. It wasn’t easily classified as biology or history. Now we know that the two are separated only by artificial academic disciplines.

Today, books such as “1493” and Jared Diamond’s “Guns, Germs and Steel show how human beings do not completely control or even understand the forces shaping our own history. The “discovery” of America was a case in point: When Columbus first stepped foot in the New World, he couldn’t have realized he would begin a reunion of ecosystems that had been separate for millions of years. And just as those effects are still being felt long after the 15th century, humans today are making decisions that will have repercussions for centuries to come. If we’re honest with ourselves, we are the most destructive invasive species of them all.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

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    Faye Flam at

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