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Thirteen winning essays from the YNA 2002 contest year

Pillbugs: Little Creatures in My Backyard

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Left: Pillbug on defense; Right: Walking pillbug



On a late afternoon last April, I strolled into the backyard to enjoy our beautiful flower garden. Much to my surprise, I found that while the crocuses, hyacinths, and tulips were nearing full bloom, there was no sign yet of our new hosta plants. I scanned the garden and finally noticed some partially eaten leaves: pitiful shreds of plant leaves dotted with holes, like some irregular green variety of Swiss cheese. My family owns no pets that could have helped themselves to this outdoor vegetable buffet. Further, the squirrels, birds, and occasional neighbors' cats usually leave our garden plants relatively undisturbed. I was at a loss for who, or what, could be hindering the growth of the hostas. 

The next morning, I discovered a swarm of "roly-polies," or pillbugs, on our hosta plants soon after the lawn sprinklers had been shut off. Hoping to control the backyard insect population, my dad wanted to spray the plants with pesticides. The family immediately protested against the idea. The backyard was our playground, and the pillbugs were friendly creatures that we could treat as leash-less, free-roaming pets. 

Garden along fence in backyard

Garden along fence in backyard


Overcome with curiosity at the missing hostas and indignant at the thought of spraying away the pillbugs, I decided to investigate pillbugs and their relationship with their environment. After collecting several pillbugs from the garden and checking out tall stacks of books and articles from the library, I sat down with my resources and embarked on an eye-opening journey into the pillbugs' world. 

Hosta plant


Pillbugs, also referred to as woodlice or roly-polies, are common backyard creatures that live in dark, damp areas, such as under stones and in bark. The humid environment helps to keep their breathing organs moist. Pillbugs typically feed on rotting wood and vegetation, but they also eat budding young plants, such as the hostas in my backyard garden. Most of the adult pillbugs that I collected measured less than 15 mm in length. The younger ones were paler and smaller. Pillbugs are not insects, for they have seven pairs of legs, two antennae, and well-developed eyes. Instead, they belong to the scientific group Isopoda, from the Latin terms iso, meaning equal, and poda, meaning foot or appendage. 

One characteristic pillbug defense against suspected predators (such as myself) is a bundle of special muscles that allows them to roll into a ball shape when touched, presenting the attacker with a "pill" of interlocking skeletal plates; hence their name, the pillbug. This mechanism likely serves to disguise the pillbug as a pebble, seed, or small clump of dirt, or to camouflage the pillbug among such objects, deterring predator attack. Contrary to popular belief, only one pillbug species is capable of this type of defense: Cylisticus convexus. A similar defense is found in Trachelipus rathkei, which rolls into a "C."

nancy9a

Nancy


I examined several pillbugs under a hand lens and noted their physical features. Their antennae are sharply angled and are attached to a broad head with four pairs of mouthparts. The pillbugs' walking appendages stem from seven main trunk segments. Following these are six smaller segments carrying specialized appendages, which my research showed to serve in reproduction, gas exchange, and excretion. I observed overturned pillbugs and discovered that the pillbugs' ventral side is a considerably lighter shade of gray than their nearly black dorsal side. Perhaps this difference is because the pillbugs need a darker backside to camouflage themselves from predators, while the underside usually remains unseen.

Nancy

For a while, I was puzzled by the observation that some "pillbugs" do not roll into a ball. I later learned from professional sources that I had in fact mistaken sowbugs for pillbugs. Through the hand lens, I noticed that the sowbugs had two long, tail-like structures at the base of the abdomen and, in accordance with my experiment, did not roll into a ball. 

Even though pillbugs look small, especially when they curl up, they can make startlingly loud noises. One night during my experiment, I had gathered around 15 pillbugs in a foam cup and left it on the nightstand in my bedroom. They climbed up the inside of the cup, creating such a ruckus with their pattering feet on the foam that I had to relocate them to the bathroom down the hall. I returned to bed in a sleepily befuddled state at being unexpectedly awakened, in the middle of the night, by none other than a handful of seemingly reticent "roly-polies." 

Pillbugs


Pillbugs' eating habits, among all the observations, was the focus of my study. Their eating habits can be helpful or harmful. Pillbugs are helpful because they ingest decayed plant material, ridding the environment of rotting plant matter. Pillbugs also help to loosen the soil as they crawl through it, making more space available for plant roots to grow. Still, pillbugs have their downsides. They seem to enjoy eating the roots, leaves, and stems of tender young plants, sometimes destroying the plant in the midst of its growth, just as they did with the hostas in my garden. Further, pillbugs sometimes infest potted plants during unnaturally wet weather, damaging the plants' roots in the process. Perhaps most exasperatingly, pillbugs may enter damp houses, especially basements, in search of food, although they cause no structural damage. 

In fact, since the day I saw the horde of pillbugs clinging to the hosta stumps, I had suspected that the pillbugs had eaten the hosta shoots. An idea gradually developed in my mind: could I possibly feed the pillbugs with typical lawn grass so that they would refrain from eating hosta leaves? A direct benefit would, of course, be to save the hosta plants while making use of unwanted grass clippings. Also important, though, are the environmental concerns involved. Society has developed such a dislike of any kind of "creepy-crawly" that farmers and gardeners everywhere have resorted to using pesticides. Often, people fail to recognize the dire threats posed by pesticide chemicals, some of which are carcinogenic and others of which are environmentally destructive.

I conceived that even though pillbugs do not usually eat lawn grass, perhaps they would eat it under certain conditions. To test this idea, I performed an experiment, hypothesizing that if lawn grass was moved to a shadier, damper area that was conducive to pillbug life, then the pillbugs would make no distinction between the grass and young plant shoots and would eat the grass instead of searching for plant shoots. 

Control Group and Experimental Group (Click to enlarge.)


As a control group, I gathered 25 randomly selected pillbugs in a 454-gram glass jar. Using an iron nail, I punctured small holes in the jar's cap and encircled the jar with a sheet of black construction paper cut to the jar's size (to darken the interior). I added to the jar five grams of damp soil and two hosta plant leaves, 3 cm by 0.25 cm. A second 454-gram glass jar, with holes punched in the cap and wrapped around with black construction paper, held 25 other pillbugs, five grams of damp soil, and two lawn grass blades, 3 cm by 0.25 cm. I kept the jars in the dark, cool area on a counter under some cabinets, and planned to observe the pillbugs and their food supply over the course of five days. On each day, I would add three drops of water to each jar to maintain moisture.

The results collected for this experiment were rather surprising. By the second day, the pillbugs had devoured all of the hosta leaves in the control jar. In the second jar, all that was left of the grass blades on the second day were the blades' stiff center fibers. This may have been because they were not able, or found it difficult, to digest firmer objects. These, too, were gone by the third day, suggesting the pillbugs' resourcefulness at sacrificing dietary preferences when their food supply ran short. When all of the plant material had been eaten, the pillbugs moved on to the mulch that had been put into their respective jars to keep themselves from starving. These observations were astonishing because I had not anticipated that the pillbugs would consume all of their food so quickly. The experiment was supposed to have taken five days; instead, it took only three.

The results of the experiment showed that while the pillbugs did accept the grass as food, they only ate the outer edges of a given grass blade, which was probably softer and easier to digest than the hard, stiff core fiber. Still, with a depleting food supply, the pillbugs eventually resorted to eating the core fiber as well. The substitution of grass for plant shoots may suggest a way to prevent the consumption of plants such as the hosta. Simply spread grass clippings around the base of a growing garden plant, as is done with mulch, to separate the plant from hungry pillbugs. The bugs will eat the grass, and the plant will stay intact.

Upon the conclusion of my experiment, I shared my results and interpretations with my dad and suggested that he cover the base of the hosta plants with a layer of grass clippings. He tried it out, and amazingly, the hosta plants gradually regained their place in the garden in late May. The grass-clipping buffer allowed the hostas to thrive in our garden, contributing to beautiful garden foliage accented with bright flowers in the summer. The garden continued to flourish until winter's first frost. 

Naturally, my experiment gives rise to a wealth of additional questions that I would like to investigate further next year. What if both the hosta and the grass were put into the same jar? Does temperature or light affect the pillbugs' eating preferences? Would the species of the pillbugs change the results? By investigating these questions, the gardening world could be changed forever.

My excursion to the backyard has had surprising and wonderful outcomes. I have learned about the fascinating world of the pillbug, a small but captivating creature. Since pillbugs are often overlooked both in everyday situations and in scientific investigations, I was glad to find that they are in fact quite worthy of study. My experiment has also prompted me to appreciate the many wonders of nature. This winter, I occasionally ventured into the backyard garden to check up on the pillbugs, for the cold weather had forced them to retreat and reduce their activity. As nature goes on, I'm looking forward to seeing them reappear, along with healthy hosta plants, next spring.

 

References

Berenbaum, May R. Bugs in the System. Menlo Park: Addison-Wesley Publishing, 1995.

Borror, Donald J., Dwight M. Delong, and Charles A. Triplehorn. An Introduction to the Study of Insects. Dallas: Holt, Rinehart, and Winston, 1976.

Bridges, Judy. "Ornamentals and Turf." Retrieved from the World Wide Web on September 20, 2001: http://www.ces.ncsu.edu

Farb, Peter. The Insects. New York: Time Inc., 1962.

Klots, Alexander and Elsie Klots. Insects of North America. New York: Doubleday & Company, 1972.

Kneidel, Sally. Pet Bugs: A Guide to Catching and Keeping Touchable Insects. New York: Wiley and Sons, 1994.

Sutton, S. L. Woodlice. Oxford: Pergamon Press, 1980.

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