Are Worms Natural? The Global Worming Debate
To be more specific, are earthworms natural? For the chronically busy and distracted, the short answer to that question is – absolutely not! Earthworms are not natural! Not even a little bit! At least they’re not natural if they’re non-native, introduced earthworms that are devouring the forest floor and radically changing the ecology of some hardwood forests in the northern United States.
Surely I must be kidding? What could be more natural and beneficial than the common earthworm, slowly churning through our compost piles and garden soils, dutifully converting organic waste into productive elements of soil? They’re everywhere. You see them when you dig in the garden. Many birds and other animals love to eat them. After heavy spring and summer rains, they cover our sidewalks and roads, and squish under the feet of the careless.
On the other hand, maybe this is just another Commie, liberal, university, leftist, socialist, hippie, environmentalist plot to alarm a gullible public and scare them into donating more money to “save the world.” Unfortunately, the truth of the matter isn’t quite that simple. Many introduced earthworms are not natural in their environmental effects and they are wreaking ecological havoc in some North American forests. Forget environmental opinion. Let’s talk science. But first, a bit of history.
Cleopatra – Worm Worshipper
Cleopatra VII was the last pharaoh of ancient Egypt, one of the most famous female rulers in history, and apparently was somewhat of a worm worshipper based upon reports that she considered earthworms to be sacred:
“Did you know the ancient Egyptians were the first to recognize the beneficial status of the earthworm? Cleopatra (69 – 30 B.C.) recognized the earthworm’s contribution to Egyptian agriculture and declared them to be sacred. Removal of earthworms from Egypt was punishable by death. Egyptian farmers were not allowed to even touch an earthworm for fear of offending the god of fertility. A 1949 study by the USDA confirmed that the great fertility of the soil in the Nile valley was due in large part to the work of earthworms.” Source: Did You Know……. Earthworms
However, Cleopatra is hardly alone in lauding the importance of earthworms to humans and the world. Aristotle called earthworms “the intestines of the soil” while Charles Darwin studied worms for 39 years and concluded that: “It may be doubted whether there are many other animals which have played so important a part in the history of the world as these lowly organised creatures.”
“It will be difficult to deny the probability that every particle of earth forming the bed from which . . . old pasture land springs has passed through the intestines of worms.”
But Blame the Pilgrims
No one knows for sure when non-native earthworms were introduced to North America, but for the sake of convenience, let’s blame the first pilgrims and colonists for starting the process of bringing in passenger and cargo ships containing rocks and soil for ballast. Introduced earthworms probably got their toehold on the continent when these materials were dumped ashore, and when plants with soil and other cargo accompanied passengers to North America.
Dang Pilgrims! There goes the neighborhood! And there goes some of Mother Nature’s magnificant hardwood forests as well.
It is just possible that John Rolfe was responsible for the worms—specifically the common night crawler and the red marsh worm, creatures that did not exist in the Americas before Columbus…
Most people know him today, if they know him at all, as the man who married Pocahontas. A few history buffs understand that Rolfe was one of the primary forces behind Jamestown’s eventual success. The worms hint at a third, still more important role: Rolfe inadvertently helped unleash a convulsive and permanent change in the American landscape….
As the colonists bitterly came to realize that Virginia had no gold and that the Indians weren’t going to selflessly provide them with all the food they needed, they began to mold the land to their needs. Unable to adapt to this foreign landscape, they transformed it into a place they could understand. In doing so, they unleashed what would become a multilevel ecological assault on North America. Their unlikely weapons in this initial phase of the campaign: tobacco, honeybees, and domestic animals. National Geographic: America Lost and Found
There is little doubt that the earthworms that you find in your yard, garden, and crawling across sidewalks and streets after rains are all non-native, introduced earthworms. In reality, they don’t belong here.
Our colleagues at the University of Idaho, Yaniria Sanchez-de Leon and Dr. Jodi Johnson-Maynard, have conducted one of the few detailed studies of earthworms in the Palouse region, and they found that three introduced species (Aporrectodea trapezoides, A. tuberculata, and Lumbricus terrestris – often called the common earthworm, or nightcrawler) dominated the earthworm community, whether samples were taken in planted grasslands in an agricultural setting or in native prairie remnants.
Earthworm Research at Washington State University
In an earlier study of earthworms, in 1999, WSU researchers Mary Fauci and Dr. David Bezdicek, of the Department of Crop and Soil Sciences, sampled earthworms at 46 sites in mostly farm fields and some grasslands in Palouse Prairie, but all of the worms they found were of introduced species. The highest earthworm diversity (8 species of non-native earthworms) occurred right here on the campus of Washington State University in the agronomy teaching gardens, perhaps illustrating the potential to bring in non-native earthworms in cultivated gardens when using plant materials originating from different sources.
So where are all the native earthworms? And isn’t one worm as good or bad as another? First, we don’t have as many native worms as you might suspect. And second, not all worms are created equal. While some introduced worms may have beneficial effects in the human-created habitats of compost piles, gardens, and agricultural systems, some of our native forest habitats evolved without any earthworms at all.
The last Pleistocene glaciation ended some 12,000 years ago (see map). Any native earthworms were destroyed by the permanent ice cover and bordering permafrost, causing distributions to be pushed to the south. It is easy to see from the map of continental ice sheets that the northeastern and north central United States were devoid of earthworms when the ice finally started melting and forests began their march northward following the retreating glaciers.
Forests in these regions have had thousands of years to evolve and develop communities of trees, shrubs, and understory plants all without any native earthworm community. And now the bad guys show up, and that would be us by the way, not the earthworms!
Worms As Ecological Engineers
Scientists have suspected for some time that introduced earthworms were having negative ecological impacts in these particular North American forests. As introduced earthworms invaded these forests, a series of largely negative ecological changes cascaded throughout the system, changing the structure, function, and even the overall appearance of the forest.
Not all worms are created equal because different species of worms occupy different habitats and eat different organic materials as food. Some species of worms specialize by living in different layers or types of soil, or specialize in eating different foods such as animal manure vs. decaying logs, vs. leaf and organic matter on the soil surface.
In the absence of native earthworms, sugar-maple and basswood forests in the northern United States develop relatively thick layers of calcium-rich duff composed of leaves and organic matter that decay slowly through the actions of fungi and bacteria. This moist, thick, rich organic layer on the forest floor supports a diverse community of herbaceous plants, fungi, arthropods (i.e., insects, spiders, crustaceans), vertebrates such as small mammals, frogs, salamanders, and birds that specialize in nesting and living on the forest floor. Many trees, shrubs, and herbaceous plants are adapted to germinate and survive under these conditions.
When non-native earthworms invaded these forests, they quickly devoured the organic layer on the forest floor and rapidly changed the ecology of these temperate hardwood forests. Scientists began to notice that as the organic layer decreased, so too did many forest floor plants, insects, and salamanders. Even the density and nest success of ground-nesting songbirds, such as Ovenbirds (Seiurus aurocapillus) and Hermit Thrushes (Catharaus guttatus), declined. Instead of a layer of duff, the forest floor began to give way to grass cover and other non-native introduced plants, that are themselves invasive.
Populations of white-tailed deer also have increased in our forests as well due to a variety of human-related factors (e.g., logging and fragmenting forests; elimination of top predators like cougars and wolves), and intensive browsing by deer further induced changes in plant communities, including threatening populations of rare and endangered plants. All of these and other impacts, such as mixing and fundamentally changing soil structure, soil chemistry, and altering bacterial and fungi communities amount to pretty impressive ecological impacts from a lowly worm!
While cause and effect relationships are complicated in ecosystems with many interacting players, scientists increasingly suspect and see evidence that introduced earthworms are intimately linked to the changing structure of hardwood forests in the northern U.S. In essence, as the forest floor disappears (is consumed by worms), the surface roots of trees and other plants are suddenly exposed to a more open, dryer, and harsher environment. A somewhat appropriate analogy is that worms end up causing gingivitis in forest communities by exposing tree roots and the forest floor.
Are Worms Natural or Not?
Natural is a relative word and the subject of debate in ecology. For some people, humans are natural, therefore anything that humans do in the world is natural and we shouldn’t worry about it. Therefore, New York City is natural. Disneyland is natural. Walmart parking lots are natural.
For others, humans long ago crossed the threshold of natural effects in the world when we began to control fire, make sophisticated tools for hunting, and then later domesticated crops and farm animals and began converting the world to agricultural production. For these people, who believe technology puts us in an entirely different category, natural means having as close to no human influence as possible.
I would answer the question about worms this way. Worms, whether native or introduced are the products of natural evolution. In that sense, all organisms are natural. However, whenever we introduce non-native species into new continents, islands, and ecosystems anywhere, then their ecological effects are not natural if and when they disrupt or change existing ecological processes and communities. In that sense, introduced earthworms in hardwood forests in the United States are not natural.
What should we do about it then? Should we attempt to kill and eliminate all introduced earthworms to save our northern hardwood forests? Hardly.
The answer to these questions is that we likely can do very little, if anything realistic, to stop the changes that are rapidly occurring in northern forests. It is not feasible to try to eradicate large earthworm populations in the soil, because attempting to do so probably would not work very well and only disrupt other beneficial soil organisms.
It also is not wise to consider introducing predators on earthworms, such as the New Zealand flatworm, which has apparently been accidentally introduced into Europe and Great Britain. Flatworms don’t discriminate between introduced and native earthworms and may cause more unintended environmental damage than they might cure by preying on native earthworms. In Great Britain, where New Zealand and Australian flatworms have been introduced, native earthworm populations have been devastated in some areas. And trying to foresee the consequences of potentially introducing yet additional predators that prey on the flatworms themselves, such as the maggots of a Tasmanian gnat, only lead to more uncertainties and ecological risks.
So where does that leave us? Should we become a nation of worm stompers and worm haters?
Currently, there are no easy answers about what to do about introduced earthworms, except for efforts to educate the general public, and especially fishers who might be tempted to dump unused fishing bait in natural habitats (see: Great Lakes Worm Watch).
Scientists will continue to study the effects of introduced earthworms, if nothing else, to better predict what changes may overcome our hardwood forests in the future. At issue will be whether the native organisms that were adapted to conditions in historical hardwood forests (e.g., herbaceous plants, insects, salamanders, ground-nesting birds) will be able to persist in this new uncertain future, and how we might try to help them survive.
Where Are the Good Earthworms?
Typical of the differences we tend to see between native species and introduced species exhibiting highly invasive characteristics, there seems to be a difference between native and introduced earthworms. There are roughly 180+ species of native earthworms in North America, but probably because they have co-evolved for thousands of years with other organisms in their respective ecosystems, they do not seem to have the dramatic or obvious negative effects that we see for newly-introduced earthworms in northern hardwood forests.For example, on Vancouver Island and the Olympic Peninsula, Arctiostrotus vancouverensis is normally found in decaying conifer logs and other cool moist substrates and is an integrated part of the ecosystem. Similarly, other native earthworms occupy a variety of habitats oftentimes south of the former permafrost line that occurred during the Pleistocene glaciation, and they have not invaded our northern hardwood forests.
The Mysterious Giant Worms
Of course our favorite native earthworm is our very own giant Palouse earthworm (Driloleirus americanus), which means “lily-like worm” because it purportedly smells like lilies. The scent, if indeed it does occur, could potentially be a chemical defense which results from handling, but most of what is stated about the giant Palouse earth is nothing more than common lore that keeps getting repeated in the popular press.
Very little is actually known about the giant Palouse earthworm, which was thought to be possibly extinct during the 1980s, until was rediscovered in 2005 by Yaniria Sanchez-de Leon from the University of Idaho while studying earthworms at the Washington State University, Hudson Biological Reserve at Smoot Hill. This “giant” worm, which supposedly could reach about 3 feet in length (although recent collected specimens are much smaller – about 12 inches or less) has been the subject of controversy as conservation groups have unsuccessfully petitioned the U.S. Fish & Wildlife Service to have the worm listed as endangered.
Dr. Jodi Johnson-Maynard, soil scientist from the University of Idaho, says that perhaps instead of the giant Palouse earthworm, we should just call it the “larger-than-average Palouse earthworm.” Either way, it’s a mysterious creature that deserves to be better known by science.
Another favorite native earthworm is the Oregon giant earthworm (Driloleirus macelfreshi). Similar to the giant Palouse earthworm, this giant worm is known from primarily 15 sites in the Willamette Valley and may reach lengths over 4 feet. However, one of our very favorite worms in the world is the threatened Giant Gippsland earthworm (Megascolides australis). These enormous earthworms apparently average about 3 feet in length, but purportedly may reach up to nearly 9 feet.
Do Worms Make Sounds?
If you’ve never heard an earthworm, you should. Just travel to Australia and try to track down one of these creatures. Or, you may watch the video below.
Global Worming Skeptics
There are undoubtedly many people who will have difficulty believing that introduced earthworms are such powerful agents of ecological change and that they could be doing harm in our forest environments. These skeptics would do well to realize that the biomass (weight) of earthworms in a productive pasture is likely much greater than the weight of the farmer’s cattle standing on top of the ground. And what happens below the ground, largely determines what happens on top of the ground.
Charles Darwin once estimated that there were more than 13 earthworms in a square meter, but we now know that productive soil may have hundreds of earthworms in a square meter and well over a million worms in an acre. The potential work of that many miniature soil bulldozers, powered by their organic fuel of decaying leaves, should not be underestimated. If you don’t believe it, start a compost pile or get a shovel and find out for yourself.
A Philosophy of Worms
I hold no animosity towards night crawlers and other introduced earthworms. They are simply natural organisms put in an unnatural place – the innocent pawns of environmental change placed there by human ignorance. It is not the worm’s fault. It is our fault. But in many cases, even we didn’t know any better when we opened Pandora’s Box and turned loose scores of unintended ecological forces now ravaging the natural world.
While I lament the loss of beauty, biological diversity, and the potential extinction of native species that may occur when ecosystems are changed by highly invasive plants and animals, it is now up to scientists and educators and the public to do better in the future. Now that we do know better, we should not make the same mistakes as our ancestors.
So the next time that you see a night crawler crossing or being stranded on a drying sidewalk, don’t stomp on it as an unnatural invader. It is simply a natural organism trying its best to survive like all other natural organisms on Earth. Like it or not, it is now part of a new natural order, created not by Mother Nature, but by humans.
While you needn’t worship the worm like Cleopatra, perhaps you pause just for an instant and appreciate the often hidden complexity and mystery of the natural world? And if you’re not afraid of such an immensely powerful creature, perhaps you even pick it up and rescue it by putting it back on some moist soil where it may resume its life. After all, a little bit of worm worship, or environmental philosophy, never hurt anyone.
For the Curious:
Wikipedia: Invasive Earthworms
MN Department of Natural Resources: Invasive Earthworms in Our Forests
Scientific American: Invasive Earthworms Denude Forests in U.S. Great Lakes Region
Online Classes, School of the Environment, Washington State University:
For those who are interested in taking online science classes and studying the types of ecology and environmental issues covered here in Nature @ WSU, you may contact the WSU Global Campus for information about:
Conservation Biology (Natrs 450 / 550) 3 cr. The science of conserving life on Earth. Dynamics of conserving biological diversity and threatened and endangered species. Junior-senior-graduate standing, next offering Spring Semester, 2015.
Restoration Ecology (Natrs 454) 3 cr., Ecological principles used to restore biological communities, ecological processes, and species on degraded landscapes. Interdisciplinary Capstone Science Course. Senior standing, next offering Fall Semester, 2015.
Environmental Assessment (Envr_Sci 444) 4 cr. Environmental impact statements and their national and state policy frameworks, methods of assessment, and team preparation of an impact statement.
The Science and Policy of Climate Change (Envr_Sci 285) 3 cr. The science of the climate system; the case for reducing greenhouse gas emissions, and the best policies to do so.
Earth’s History and Evolution (Geology 210) 4 cr. Introduction to Earth’s history and evolution through observations, data collection and analysis, readings, and writing exercises.
The Environment, Human Life, and Sustainabiltiy (Envr_Sci 101) 4 cr. Interactions between humans and their environment; multidisciplinary introduction to environmental concepts and concerns.