The earthworm is one of those animals that everyone recognizes. We find them, sometimes in huge numbers, when we dig into our soil. We find them squirming over sidewalks and patios in the morning, or after a rain, and too often find large numbers of dead ones on sidewalks exposed to the sun, victims of desiccation when they did not get back into the soil in time. They are raised as a crop to sell to gardeners, for fishing, and likely as a food resource for some cultures around the world. They are used, sadly, as props for some of the outlandish TV shows where contestants lie in piles of them or put gobs of them in their mouths. Who among us has never heard "the early bird gets the worm"? They go by various names, such as angleworm, earthworm, night crawler, red worms or manure worms. They may be small ones in your garden only a couple of inches long, or some of the spectacular species found in Australia, Africa, or South America that purportedly get as long as 20 feet. Imagine hooking one of those onto your fishing line. In the United States there is even one extremely rare species that grows to 3 feet in length. It is known from Oregon, but has not been found for many years. There are as many as 3000 identified different species around the world.
Earthworms eat dirt. More accurately they feed on organic matter in the soil, including bits of material from the soil surface such as the clippings and thatch on lawns, dragging these down into their burrows for ingestion. Some amount of soil goes in as well, and when it comes time to excrete their waste material some kinds head to the surface to eliminate the excess, depositing their fecal matter as small mounds. This often occurs on fine, managed turf, such as golf courses, and as the mounds grow within and on top of the grass it creates some substantial problems. Some of these are just aesthetic, in that a long fairway with that even, carpet appearance now has thousands of piles of dirt ruining the view and affecting play. The crews that maintain this sports turf have additional problems when they mow the lawns, as the piles of dirt get chopped by the mower blades, dulling the blades much more quickly than necessary. At times these fecal accumulations dry to a very hard consistency, making it even more difficult to mow.
Most kinds of earthworms will not create these surface piles of castings, but deposit their waste material within their burrows. Only a few become the nuisance, such as a kind most often called a "night crawler" - Lumbricus terrestris - a species found across the U.S. that is a primary culprit. With millions of earthworms living under any acre of turf it is estimated that as much as 25 tons of soil is brought to the surface annually for an acre of ground. This work is a vital component of healthy soil, aerating the soil and turning it to prevent compaction. The feeding activity recycles dead vegetative material quickly, preventing a buildup and returning the nutrients to the soil as food for growing plants. As homeowners many of us are willing to pay for this service, contracting to have a landscape company aerate the lawns mechanically. Their equipment removes plugs of soil to allow oxygen and water to better enter the soil profile, with the plugs then chopped up with the next mowing to return the nutrients. Earthworms are willing to do this for free.
Homeowners will often find earthworms crawling about on a sidewalk, and there is conflicting information on exactly why this happens. Some articles will tell us that the worms are driven out of the ground when it gets too saturated with water, such as during extended rains or when turf is heavily watered. The belief is that the worms are subject to drowning if they stay in the soil. Another authoritative website tells us that earthworms are perfectly comfortable living in extremely wet soils, and that drowning is not an issue. Their reason for surfacing during these wet periods is for migration or mating, moving across the soil surface to get to new places. Those that are found dead on sidewalks likely were still exposed there when the sun came up, and died from the heat, direct sunlight, or dehydration.
The earthworm is well adapted for living in the soil, and has been around doing so for at least 90 million years. It moves through the soil by creating a tunnel ahead of it, digging with the help of a shovel shaped area on its head. When the worm detects a fissure in the soil it pokes this shovel in and scrapes away dirt until it can move ahead. The body is covered with microscopic hairs that help it to move forward, as well as a coating of lubricant that reduces friction. Their mouth is also at the front of the head so that they can eat soil as well as displace it, taking nutrients from the soil and excreting the remainder. They breathe through their skin with specialized organs that exchange oxygen from the outside with waste gases from inside, and must remain moist for this to take place. They have sensors on their bodies that detect light, and they quickly move away from light which would indicate they are exposed and vulnerable.
Earthworms are not without their enemies, the avid fisherman notwithstanding. A great many animals find earthworms to be a highly desirable and available food source. Perhaps this is one purpose for their existence in Nature - to help sustain other organisms. Among these predators are birds, ants, snakes, frogs, toads, lizards, beetles, and fish. The earthworm is the major part of the diet of moles that burrow through the soil. In Africa there is even an earthworm species known to eat other earthworms. There are some parasites of earthworms as well, and one profiled in another BugInfo article is the flatworm called a Land Planarian, an exotic import native to the Australian regions of the world. Another common parasite is a fly larva, or maggot, of the Cluster Fly. Unlike most pest flies around our homes, whose larvae feed on decaying materials and dead animals, the Cluster Fly deposits its eggs on the soil. The maggots then seek out and enter the bodies of earthworms, feeding within them until they are ready to pupate and become adult flies.
There are some myths about earthworms. One is that you may cut it into pieces and create a bunch of new earthworms. This may work with starfish, but not with earthworms. The section that contains vital nerves and organs may survive for a time, but it will not be healthy and will not produce offspring. If only a small portion of the worm's body is removed it can regenerate that part, although, oddly, if the tail end is removed it may grow back as either a head or a tail, and if it is a second head the worm is going to starve. It is true, however, that an earthworm contains both male and female parts. This is another area where you will find conflicting information available. Some articles tell us that they will normally mate with another earthworm, but if necessary can produce fertilized eggs and young by themselves. Other articles agree that both male and female parts exist within a worm, but that it is physically unable to fertilize itself, and must mate with another individual. Apparently these subterranean creatures are still somewhat misunderstood. Mating is a second reason that earthworms will come out of the soil, finding it easier to locate a mate above ground.
Most of us cherish our populations of earthworms in our gardens, and may encourage their growth by burying a lot of plant materials to increase the organic matter available. For those who suffer the negative consequences of earthworms, and their hard piles of fecal matter on the surface of lawns, the question is asked "how to control them?" This is not an easy question to answer, and in fact at this time there are no effective methods for reducing the earthworm population in any area of soil. There are no pesticides of any kind labeled for use against earthworms, and while you may be able to read of concoctions on the internet, or suggestions of certain insecticides that will kill the worms, this is not legal and is contrary to a healthy soil profile. The worms provide such tremendous benefit that, even with the minor problems they create, they are far more helpful to a lawn that they are a problem. When bothered by the little piles of dirt on your lawn the best control at this time may be to accept the benefits those little piles represent, and rake over them to distribute that soil.