Exploring Earthworms' Influences on a Miniature Ecosystem
When you're like me and you live in a place like New Orleans, bugs are pretty much a part of everyday life. If you walk outside for more than five minutes, regardless of the season, your skin gets freckled with mosquitoes, and everywhere you look, there's an aura of gnats surrounding the sago palms. Dragonflies flit and float around plants and pools, and ladybugs wander in aimless loops around our ceilings while we're trying to get to sleep. And while these peculiar six-legged invertebrates may not necessarily be beautiful, they certainly are part of what makes New Orleans what it is. After all, spring just isn't the same when you don't have to cautiously dodge those thorny, neon-green caterpillars sprawling lazily on the gecko-gray sidewalks.
The other day, as I perched on the wide slate wall of the terrace in my backyard, I slapped a mosquito that had just come to a landing on my knee and looked out at the spectrum of paper-thin, satin-soft flowers; the bouquets of long, glossy green ginger leaves; and the young live oaks, which were still awkwardly supported with wires and poles all around their skinny trunks, taking in the array of such a diverse ecosystem. As I watched a tiny doodlebug slowly span the leg of a lawn chair, quickly rolling itself into a protective ball at the slightest flinch of my toe, my mind shifted—the wide stretch of grass seemed big to me. How big must it seem to one of the white, microscopic grains-of-sand-with-legs crawling around on the fig ivy? Furthermore, what was I living with? Which bugs ignored me from their tall posts in the holly tree as I walked through the grass? How many macroinvertebrates, with long Latin names more conspicuous than their bodies, hid out under the crunchy yellow leaves that had been discarded by the dusty magnolia tree in the corner of our yard? And what, exactly, was sifting through the soft, velvety-smooth soil beneath my toes, oblivious to the fact that I was separated from them only by a thin layer of grass that had yellowed from the wet New Orleans cold?
After trekking through my backyard, sifting through dead leaves, and swooping a clean peanut butter jar after passing butterflies and bees in a vain effort to find a few bugs to research, I decided to abandon my original quest to find as many different species of insects as I could. Instead, I began exploring aimlessly, hoping I might find inspiration in some other part of my yard. Armed with a rubber-handled trowel and an armful of tall glass jars, I gingerly walked my way through the muck, pausing on the occasional island of dry grass to dissect the ground in my search for insects. The wide dull blade weakly pierced the ground, and I quickly looked underneath in hopes of catching at least a glimpse of some brightly colored foreign beetle before it made a quick getaway. Instead, the claylike cake sprinkled with grass yielded a tangled knot of wriggling worms. Tiny clots of soil clung stubbornly onto the long, ridged bodies that were so pink and glossy they looked almost raw. I paused, watching the dirt in fascination as the earthworms continued about their business, digging out neat little tunnels just big enough for them to squeeze through as they went along. I piled a few of the worms onto my shovel and emptied them into an old pickle jar, then walked about 12 feet on, where I made another quick stop to sample the soil.
Again, I immediately came across signs of life. In fact, my shovel brought back another tightly woven nest of worms—but these, although they were about the same length, were much thinner, and they were all a coral pinky-red. Digging a little deeper, I only came across more of these stringy, yarn-thin worms. This led me to wonder a bit more about these fascinating things. What were these two different species, and why were they completely isolated from each other? Why did one species live 12 feet away from the other; why weren't any of them "mingling"? Which niches did each species occupy, and, if put in the same environment, how would they interact—would their interaction result in commensalism, mutualism, or parasitism? I realized that I was most interested in learning more about these strange, legless things that ate creatures in the dirt and flossed their way through the underground, so I emptied my subterranean findings into a wide plastic container and set to work.
It didn't take much searching to find that the thicker earthworms that I'd found first were known as Lumbricus terrestris, or the common earthworm, sometimes called a nightcrawler. And although I couldn't find the red-yarn worms on the Internet or in any books, I suspected that they were the babies of the same species. I inferred further that the red-yarn worms were isolated from the nightcrawlers until they matured.
As with all other organisms, these earthworms occupy a certain niche: They are both decomposers and consumers, feeding on things like decomposing remains, manure, and other small underground organisms like nematodes, bacteria, fungi, and rotifers. Some species of earthworm, like the nightcrawler, can also get nutrition by emerging from the soil at night and taking leaf litter back down with them. Although they don't have teeth, they do have very powerful mouth muscles that enable them to eat. Predators include birds, moles, toads, and centipedes, and certain species of mites can parasitize the cocoons or the worms themselves. Earthworms breathe by coating themselves with mucus, which allows dissolved oxygen to pass into their bloodstream, so living conditions must be moist and humid, or else the worms will dry up. They are ecologically important because they loosen and mix up the soil, enabling water and nutrients to seep through to plant roots. Since they can't walk, earthworms move with tiny bristles, or setae, which are paired on each of their segments and grip onto the worms' tunnel walls. Then the worms push themselves forward with strong muscular contractions (Columbia Encyclopedia).
The nightcrawler lives all over the world, except for arctic areas, and its life expectancy ranges from 850 days to six years from birth to death. It takes approximately one year for these worms to mature—at maturity, a worm develops the clitellum, a swelling around the middle of the body that produces reproductive organs. Earthworms are hermaphroditic, meaning that both male and female sexual organs grow in each worm. However, an egg from one worm must be fertilized by the sperm from another one. To procreate, the clitellum is shed off to form a cocoon, and as it is shed, it picks up eggs and sperm from different segments of the worm's body. When first created, the lemon-shaped cocoon is very soft and sensitive, but it quickly becomes leathery and tough to protect the baby worms inside.
This information fascinated me, motivating me to dig deeper (both literally and figuratively), with more specific questions. How did a worm know when it was time to emerge out of the ground? Did their bodies operate on a certain "clock"—for instance, when it was 11 at night, did they all surface from the soil, simultaneously gather as many leaves as could possibly fit into their tiny mouths, and then silently sink back down into their tangled town of tunnels? Perhaps the worms could sense the nightly temperature drop, or maybe, because of their sensitivity to light, they could tell when it got dark. If so, would the worms get "confused" and surface at unusual times in cold temperatures or on cloudy days? Also, in addition to leaf litter, could the worms help biodegrade other materials (for example, orange peels or bread crumbs)? I had so many questions about these curious creatures and their importance in ecosystems that I finally decided to research these worms as a whole in their new plastic environment—or the "worm cage," as my brother affectionately called it—in a sort of expedition without one fixed question.
To start this research, I went into the backyard and shoveled about two or three more cups' worth of soil into my container to dilute the high saturation of worms and create more of a balance. Then I brought it inside, loosely covering it with a sheet of Saran Wrap that had been pierced with holes to keep anything from accidentally falling out, and rested it on an empty shelf in the kitchen that was high enough to keep my dog from getting into it but low enough so I could constantly check on it. It was in a central location where I wouldn't accidentally neglect it. To make the environment more "real" and help the worms adjust, I monitored the weather and imitated it in the container—for example, if it rained heavily, I would fill a cup and saturate the dirt; if, however, it was sunny and dry for three days in a row, I would leave the soil as it was.
One morning as I was busily flitting around the house to get ready for school, my eyes darted over to the container resting on the shelf. I hadn't planned on giving my research any thought at such an early hour, but I looked twice at the wide, transparent plastic and took a step closer. There were five lean stubs of grass, pricking their pale white-green heads out of the barren mud like stubborn feathers poking out of a goose-down pillow. They weren't more than one or two centimeters long, but I was amazed that only two inches of soil could provide an environment fertile enough for grass.
I kept a close eye on the container after I noticed these tiny shoots of grass and was able to watch as they grew in height and abundance. Once or twice daily, I just sat for a while and stared at the grass, in the childish and unrealistic hope that I could watch it grow, watching the damp dirt slowly inhale and exhale as glossy gray worms wove their way through the shallow maze of tunnels. A week after the grass discovery, I checked back, this time armed with a ruler. The five tiny buds from the week before had grown to six-inch stalks and had multiplied by a whopping 500%—I could now count 25 shoots peeking out from the black earth—and, to prove the process of photosynthesis, 23 of the 25 stalks of grass had grown on the side of the container that was closest to the sun.
As shown in the graph, each stalk of grass recorded followed a similar growth pattern—for each one, the height was multiplied by approximately 9.7 times between December 16 and December 23. From this information, I hypothesized that earthworms were a major influence on grass growth. Due to time constraints, a control group could not be set up with just plain soil and no worms in a similarly sized plastic container. While it would have been a great help to further support my hypothesis and confirm that earthworms are indeed beneficial for plant growth, I felt that the data would be skewed, as the original container had ample time to fertilize and grow plants, whereas the control group would have a much more limited amount of time, therefore giving the original container an unfair advantage. However, I did take several soil samples in various places to explore areas that were similar to the said control group: my backyard, which had very lush grass; my aunt's backyard, which was very barren and had dry, brittle grass; and my front yard, which had fairly healthy grass, although it wasn't nearly like the long, soft grass in the backyard. In my backyard there was a very high population of earthworms, as well as other subterranean insects such as centipedes and several species of beetles. In my aunt's backyard, I couldn't find any worms, and in my front yard, there was a much lower population of worms and a less diverse community of beetles. Although all sampled areas were in the same condition, it was obvious that the amount of healthy green grass increased where there were more worms, which supported my hypothesis.
Although some of the tests and procedures I ran brought back useful information, some questions were left unanswered or produced unexpected results. For example, in a small experiment, I scattered 10 small bread crumbs, 10 fallen leaves, and 10 small pieces of an orange peel over the soil to see if earthworms assisted in biodegrading. Research in books and the Internet told me that worms rose out of the soil at nighttime, taking leaf litter back down with them. So when I started the experiment, I expected the worms would definitely eat the fallen leaves, even if they didn't eat the bread crumbs or the orange peels. However, after checking back the next day and again a few days later, not one of the small leaves, bread crumbs, or pieces of orange peel had been touched. Perhaps the environment in the container was so different from the deep expanse of soil outside that the worms didn't follow the same habits as they had before. Maybe the worms were so new to the container environment, they hadn't yet created permanent "homes" in which they could eat their food. Or it could have been a combination of these two factors.
Among various other expeditions and small tests (there's not enough room to go into detail for all of them!), I learned much more about earthworms and this ecosystem as a whole than I had ever expected. For example, the color of an earthworm is not affected by its food. Among the common reddish-brown and grayish-pink worms I found, I also came across two or three olive-green worms. Contrary to my hypothesis that these worms had been eating more leaves and grass and were therefore greener, I discovered that they were a completely different species and genus—Allolobophora chlorotica, native to Great Britain. And while I realize that my results are not infallible, and that I needed a proper control group to really show the difference worms make in plant growth, I feel I made a huge amount of progress in learning about the importance of earthworms to any ecosystem.
Exploring a subject so new to me not only taught me important things about ecosystems and nature (not to mention preventing bug bites the size of a nickel), but it also changed my personal views about nature. Two months ago, if I came across an earthworm inching its way across the sidewalk, I would have ignored it and walked around it. But now that I realize how important they are for not just underground life, but also for the plants and trees that are so important on this side of the grass, I bend over and, unfazed by its slimy body, pluck it up and drop it into a shady garden. So next time you eat a crisp chopped salad, receive a bouquet of flowers, enjoy the shade of an ancient oak, or inhale the sweet, raw odor of freshly chopped grass, thank the worms, your very own natural farmer, fertilizer, and plow.
Earthworm. Encyclopedia.com. HighBeam Research, Inc. Retrieved 19 December 2004 from the World Wide Web. http://www.encyclopedia.com/html/e1/earthworm.asp
Earthworm—Lumbricus terrestris. University of California at Davis. Retrieved 23 December 2004 from the World Wide Web. http://www.sarep.ucdavis.edu/worms/profile6.htm
Fox, Richard. Lumbricus anatomy. Richard Fox, Lander University. Retrieved 14 December 2004 from the World Wide Web. http://www.lander.edu/rsfox/300earthwmLab.html
Ingram, Bob. Earthworm Benefits. Trinity Ranch. Retrieved 16 December 2004 from the World Wide Web. http://mypeoplepc.com/members/arbra/bbb/id19.html
Journey North Teacher's Manual. Journey North. Retrieved 30 December 2004 from the World Wide Web. http://www.learner.org/jnorth/search/Worm.html
Safra, Jacob E. "Earthworms." Encyclopedia Britannica. Encyclopedia Britannica Inc., 2002.
More About This Resource...
This winning entry in the Museum's Young Naturalist Awards 2005 examines how earthworms interact with their environment. Remy's essay—with charts, photographs, and a reference list—details:
- her backyard observation of earthworms "digging out neat little tunnels just big enough for them to squeeze through"
- an explanation of how earthworms are both decomposers and consumers
- the series of questions prompted by her initial investigation, including "How did a worm know when it was time to emerge out of the ground?"
- what she learned about the importance of earthworms to any ecosystem
Less than 1 period
Supplement a study of biology with an activity drawn from this winning student essay.
- Send students to this online article, or print copies of the essay for them to read.
- Have them explain in their own words what Remy meant when she said you can think of earthworms as "your very own natural farmer, fertilizer, and plow."