Slimy, slippery, pinkish, or salmon-colored earthworms are familiar to just about everyone. They are segmented worms with numerous concentric ridges, one for each body segment. The clitellum (the ringlike collar about a quarter of the distance from the head) is typically pink, swollen (raised higher than the rest of the worm), and partially encircles the body.
The movements of these animals are usually slow — wriggles and stretches. In their burrows, earthworms move forward by extending the front part of the body forward, then pulling the rear portion after it. Tiny, bristly hairs (setae) that point backward help the worm grip the burrow, preventing the front portion from sliding backward when it draws the rear part of the body forward.
Sign: Our most familiar earthworms create neat, lumpy piles of castings that resemble small, rounded chimneys to their burrows. The soil otherwise looks normal (not granular like coffee grounds, which is the sign of Asian jumping worms).
Some common nonnative species include:
- Nightcrawler or common earthworm (Lumbricus terrestris)
- Red earthworm (Lumbricus rubellus)
- European nightcrawler (Eisenia hortensis)
- Red wiggler, manure worm, or redworm (Eisenia fetida)
- African nightcrawler (Eudrilus eugeniae)
Native North American earthworms include:
- Diplocardia spp. are in the family Acanthodrilidae.
- Bimastos and Eisenoides spp. are in the family Lumbricidae.
- Sparganophilus spp. live in muddy habitats, such as near rivers and streams; they are in family Sparganophilidae.
Nonnative, invasive jumping worms (Amynthas and Metaphire spp.) have been receiving a lot of press, and for good reason. Identify them by their smooth or silky (not slimy) skin; grayish or brownish, sometimes iridescent color; creamy white clitellum that is not raised and completely encircles the body; and wild, thrashing movements. Where they are numerous, the soil resembles coffee grounds or ground-beef taco meat. They alter soil chemistry and structure and disrupt native ecosystems literally from the ground up. They also damage lawns and landscape plantings.
Similar species: Earthworms (there are many families) are in phylum Annelida, a large invertebrate group also called the segmented worms or ringed worms. All have a segmented body plan, with each segment containing the same set of organs as the ones next to it. Externally, you can see each segment as a separate ring-shaped ridge separated on either side by an indented furrow. The first and last segments are different; the first contains the mouth and the last contains the anus.
Other annelild worms you might be familiar with are:
- Leeches, which are a group of flattened, parasitic or predaceous worms found in freshwater habitats. They are common in Missouri's ponds and lakes.
- Among saltwater annelids, the tubeworms, feather duster worms, and Christmas tree worms are common in marine aquariums. They do not live in Missouri.
- The Bobbit worm is another marine annelid that has gained a lot of attention on social media, because of its voracious, lie-in-wait, predatory biology. This oceanic worm does not live in Missouri.
- Ragworms, clam worms, bristleworms, and fireworms are more saltwater annelids you might see if you visit a coast; they have rows of bristles and/or leglike extensions running down the sides. Take care with these species, because these groups tend to have bristles that can deliver a painful, venomous sting, or sharp mouthparts that can pinch hard. They don’t live in Missouri.
Adult length: Varies by species. One of our largest earthworms is the European nightcrawler, which commonly reaches 6–8 inches.
Habitat and Conservation
You might be surprised to learn that our most familiar earthworms and nightcrawlers are not native to North America. Like the dandelion and white clover so familiar in our lawns, they were introduced to our continent long, long ago. They arrived with European settlers.
About 175 species of earthworms are found in North America. About 60 of them — about one-third of North America’s earthworm species — are not native to North America but were introduced here from Europe or Asia. Most of our native North American species are unfamiliar to most people.
During the most recent glacial period, about 20,000 years ago, massive ice sheets moved southward from the Arctic to cover much of North America, including much of Canada, New England, the Great Lakes region, the Dakotas, and the northern half of Missouri. The ice scoured the soils from the land, leaving bedrock beneath. Earthworm species that had lived in those regions before the glaciation apparently were mostly wiped away or were frozen to death by centuries of permafrost. Earthworms do not disperse very quickly, so the earthworms that survived in southern regions did not repopulate the glaciated lands. Thus, for thousands of years after the glaciers retreated, the formerly glaciated landscapes of North America had few or no native earthworms. The non-glaciated regions are the only parts of North America that still have native earthworms.
Settlers from Europe introduced European earthworms to our continent as early as the 1600s. The earthworms apparently arrived in potted plants and/or in soil used as ship ballast. These worms have been spreading in North America ever since — mostly due to people moving them when they move soil and potted plants. In northern, glaciated states, where earthworms had not been present for thousands of years, the introduction of nonnative earthworms has changed and is changing the characteristics of forest soils, with an overall negative effect on native forest ecosystems.
The very characteristics of earthworms that make them so beneficial to gardens and compost heaps makes them a problem for native forests. In gardens, people want loose, aerated soil with organic materials quickly broken down, making their nutrients available for growing plants. In native forests, however, trees, wildflowers, and other forest plants and animals have evolved to thrive where the soils are covered with a thick layer of leaf litter, twigs, and other detritus that does not break down quickly. The earthworms’ presence makes the soils more hospitable to nonnative and invasive plants.
Eating is what earthworms do, and different species forage in different soil depths and have different effects on the soil. Their feeding habits are a key to understanding their effect on the environment.
- Epigeic species live at or near the soil surface, feeding on leaf litter (dead leaves or other dead plant material) or animal droppings. These species tend to be pigmented with brown and are not very large; 3–4 inches is the usual size. Not many native earthworms are epigeic (epp-uh-JEE-ik); most epigeic worms in North America are nonnative, and some pose serious problems as invasive species that damage native habitats.
- Endogeic species live deeper underground, feeding on organic matter in soil. Endogeic (EN-doe-JEE-ik) species tend to be unpigmented: pale pink or grayish; you can often see the soil they’ve eaten inside them. Our native Diplocardia species are an example.
- Anecic species live in well-established, deep, vertical burrows that are fairly permanent. They feed at the surface and tend to be large. One well-known anecic (uh-NEE-sik) species is Lumbricus terrestris, the common nightcrawler, introduced here from Europe. It commonly reaches 8–10 inches long and eats dead leaves at the soil surface, sometimes dragging the leaves down into its burrows. A population of them can eat away all the dead, fallen leaves from an area by springtime.
Are nonnative earthworms good or bad for the environment? The answer is complex and depends on the region, type of habitat, and type of worm.
Some nonnative species are causing great damage to native habitats or to human economic interests, especially in forests of glaciated regions to our north.
Because of their extreme effect on soils, the invasive jumping worms are a major concern anywhere they appear on our continent.
Meanwhile, in unglaciated parts of North America, such as southern Missouri and the southeastern United States, where a variety of native earthworms have lived for thousands of years, the long-established nonnative species are less of a concern. In cases where the nonnative species have been established for hundreds of years, it is difficult to determine the impact they have had on landscapes prior to European settlement.
There is no good way to eliminate only certain types of earthworms once they are established in an area.
Whenever possible, it is best to prevent the spread of nonnative earthworms into native natural habitats, where they change soil characteristics, damage plant communities, and outcompete native earthworms.
Earthworms are hermaphrodites: each individual possesses both male and female reproductive organs. Adult earthworms develop a collarlike glandular swelling called a clitellum about a third of the way down the body. Two earthworms mate by exchanging sperm with one another. Later, the clitellum of each worm secretes a mucous material in the shape of a ring around the worm. The worm backs out of the ring, depositing its eggs and the stored sperm into the mucous ring. As the worm exits the ring, the mucus seals itself into a rounded, onionlike shape; this egg case is called a cocoon. Some weeks later, the young hatch and begin their lives in the soil. The young worms look like tiny versions of the adults, but lack the clitellum.
Some species of earthworms are parthenogenetic, where eggs develop into young without fertilization.
An earthworm has the same number of body segments its whole life long. It does not add segments as it grows. Many species can heal and regenerate if cut in two.
The activities of humans have hastened the expansion of nonnative earthworms. People move worms on purpose or inadvertently. Anglers have transported worms into natural habitats; gardeners have moved them in compost and within potted plants; construction workers move them in soil stuck to excavating equipment. It is best to make an effort to avoid introducing earthworms into natural habitats.
Fish bait: Earthworms are so popular for catching fish, anglers even have favorite techniques for catching the worms. Many people have compost heaps where they can reliably find plenty of worms and grubs. But earthworms bought at shops or found in your compost heap are almost certainly nonnative. Please do not release bait into natural habitats.
Earthworms are important players in the decomposition process. They eat decaying vegetation and other organic matter, then poop it out as a nutrient-rich, soil-like material called castings. Anyone who gardens or has a compost pile can appreciate the way earthworms can rapidly break down potato peelings, yard waste, and strawberry hulls.
People in the Old World have valued earthworms for ages. Cleopatra was said to have made it illegal to transport earthworms from Egypt’s soils. Aristotle called them the “intestines of the soil.”
In his old age, Englishman Charles Darwin studied earthworms intensively and demonstrated how, over time, they turn over the soil like a plow, making it more fertile. He stated that he “doubted whether there are many other animals which have played so important a part in the history of the world as have these lowly organized creatures.” His last book was The Formation of Vegetable Mould, Through the Action of Worms, published in 1881. In Victorian England, a nation obsessed with gardening, it was a bestseller. Before its publication, many gardeners considered earthworms as pests, but he showed they were valuable.
Worms are important metaphorically. We’ve all heard the proverb “the early bird gets the worm!” English literature is also full of mentions of worms as grim symbols of decomposition after death. As Shakespeare pointed out, “A man may fish with the worm that hath eat of a king, and eat of the fish that hath fed of that worm.” Also from Shakespeare, Mercutio’s dying words: “They have made worm’s meat of me!” Worms are also symbols for the lowliest, weakest, and most downtrodden of people: “tread on a worm, and it will turn!”
Earthworms played a role in the development of one of the world’s great faiths. A young prince named Siddhartha Gautama, born about 500 BCE in present-day Nepal, is said to have attended an annual community plowing ceremony, celebrating the planting of crops. Amid the festivities, he noticed that the plowing had exposed earthworms, and that birds were devouring them. He sought to reconcile the earthworms’ fatal struggles amid the joyful occasion. His meditations on the universality of suffering and the importance of compassion led, in part, to the philosophy of Buddhism.
Earthworms are popular for dissections in biology classrooms, where students learn some basic invertebrate anatomy and physiology, which can be applied to other animals, including ourselves.
Earthworms are high in protein and other nutrients, and globally, many people eat them. Like any other meat, they should be cooked. Do some research; learn how to remove the dirt from their digestive tracts and how to prepare them safely. Avoid worms that may have come in contact with pesticides or other potentially toxic substances.
People have invented ecologically friendly vermifilter toilets, which are purported to be better than standard latrines by decomposing human excrement via a colony of composting earthworms. The resulting worm castings can be used to improve soils for agriculture.
There's an entire ecosystem in the soil. The study of soil ecology, including earthworms and their interactions with living and nonliving components of the environment, is a critical and expanding area of science. The field has great implications for agriculture, conservation of native habitats, climate change, global hunger, and public policy. If you're considering a career in science, this could be a field in which you can make a real difference.
The soil itself is a kind of habitat. What looks like “just dirt” to us is full of organisms — bacteria, fungi, microscopic roundworms, small insects, mites, and yes, earthworms — that break down and recycle organic materials, aerate the soil, and make soil permeable to rainwater. The ecosystem within healthy soils is what makes plant life and animal life (including us) possible. Topsoil degradation and infertility is a major cause of hunger and poverty in the world.
In or on top of the soil, earthworms can deposit more than 1,000 metric tons of fecal material per hectare annually. Their burrowing creates vast networks of tunnels in the soil, changing its structure, allowing air and water to penetrate into the earth. They are constantly moving the soil, having both subtle and large-scale effects.
In a compost heap, where we want our kitchen scraps and yard waste to break down rapidly, earthworms are a boon. But in natural habitats, where trees and wildflowers are adapted to soils covered with fluffy layers of fallen leaves that take a long time to break down, nonnative earthworms chew up that natural mulch too quickly, to the detriment of native plant communities.
The most striking effects of nonnative earthworms appear to be in forests along the northern border of the United States and Canada. Those native forest communities are adapted to soils without the presence of earthworms. With the spread of nonnative earthworms that eat up the protective, mulchlike layer of leaf litter, the forest floor no longer supports the growth of native wildflowers, tree saplings, and other low plants and is more susceptible to erosion. Rare plants are disappearing. Nutrient cycles are disrupted.
The appearance of invasive nonnative jumping worms (Amynthas and Metaphire spp.) in northern forests that were already damaged by nonnative Lumbricus earthworms amounts to a second, much more harmful hit to those ecosystems.
Countless animals eat earthworms: moles and shrews, toads, frogs, salamanders, turtles, lizards, snakes, birds, fish, and more. Many animals feed earthworms to their young. Gartersnakes, brownsnakes, and red-bellied snakes eat earthworms; ring-necked snakes, earthsnakes, wormsnakes, and lined snakes feed almost exclusively on earthworms.
While nonnative epigeic (leaf-litter-eating) earthworms provide food for many native animals, they also disrupt the animals’ overall habitat by eating up the leaf litter and altering the forest plant community.
The American robin is one of the most common birds in North America. Its numbers may have increased since European settlement due to the spread of nonnative earthworms, which tend to live at or near the soil surface. Some scientists hypothesize that a northward expansion of woodcock territory might be related to the introduction of nonnative worms into Canada.