Millipedes and Their Defense Mechanisms
The class the millipedes are in, Diplopoda, is intriguing because it is thought to be one of the first animals to make the transition from water to land. Our lab group sought to find out under what circumstances and how millipedes use defense mechanisms. Do the millipedes curl up into a ball to evade predators? Do they bite predators and prey to inject a venom? Do they have a camouflage coating? These questions were answered by our lab experiment. We took three different groups of millipedes and divided them by an external stimuli and looked for a response. The stimuli were a large wolf spider and a gentle probe.
We placed the millipedes in separate containers and looked for any signs of defense. The results were a little shocking. The millipedes ignored the stimuli as if they did not feel a threat. Interestingly enough, this is because millipedes have very few natural predators, so they have little instinctive fear. Also, they do not need to inject poison into a predator or prey, because they are detritivores. Introduction Interactions among species play a crucial role in the energy flow and chemical cycling of an environment. These interactions can form competitive, symbiotic or predatory relationships among organisms.
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In predator-prey relationships, prey employ various defense mechanisms against predators in order to increase the chances of survival and reproduction. The same hold true for millipedes. Millipedes, members of the class Diplopoda, are nocturnal arthropods. Millipedes have segmented bodies with a pair of legs on each segment, and range in colors from brown to bright green. They inhabit a variety of forested environments worldwide, particularly in dark and damp microclimates underneath rocks and soil, where they consume decaying plants (Rowland, 2009).
Millipedes are descendants of insects that appeared on land over 400 million years ago. They are thought to be one of the first animals to make the transition from water to land. Their ecological role has remained unchanged since their first appearance as detritivores living on the forest floor (Kime, 2000). As detritivores, millipedes eat decaying plants as a source of food and face predation from lizards, birds, and scorpions by having a strong exoskeleton. As a result, millipedes employ defense mechanisms of curling up into a coil or release toxic chemicals when threatened.
By curling up, they are able to protect its legs and head while exposing the sturdy exoskeleton. The secretion of hydrogen cyanide and other toxins is used in some species if curling up does not work. The aim of this study is to observe the defense mechanisms of millipedes and how they are employed for survival in their habitat. Understanding its defense mechanisms allows for us to understand the importance of a millipede within an ecosystem as a decomposer and nutrient recycler. Methods The purpose of this experiment was to study the defense mechanisms of millipedes in different environmental situations.
In our experiment, we used three millipedes (Narceus americanus) to test this. Narceus americanus, or the North American millipede, is usually gray in appearance and four inches long. Each millipede was placed separately into containers similar to that of its natural habitat, with moist soil, rocks and decayed leaves. The first container was used to study the millipede’s response to being gently poked with a probe. The second container was used to study the millipede’s response to the presence of a spider, a predator. The third container served as a control, with the millipede being unaffected.
For the first container, the millipede was gently poked with a probe and we counted the number of pokes it took to elicit a response. We also measured the amount of time in which it took to do so. That took place three times every five minutes. For the second container, one group member introduced the spider into the container, and once again we measured the amount of time it took for the millipede to respond. For the sake of preserving our organism for the next trail, we removed the spider before it attempted to eat the millipede.
In the third container, one group member observed the millipede’s behavior in its natural environment. We had two separate trials a week apart. Results Figure 1: Average Percentage of Response to Poking Days 1 & 2 Figure 2: Average Rate of Response During Spider Exposure for Days 1 & 2 by Number of Approaches Discussion We expect our results to be a quick response from the millipedes under both conditions. We believe that the millipedes would have responded faster to the presence of the spider than the poking of the probe.
We thought this because the spider can inflict more potential harm. During the second trial of the experiment, we expected to observe a faster response with repeated exposure to the probe. Repeated exposure to the probe did not elicit any different results. It was highly unlikely that the millipede in the control container would employ any defense mechanisms. It was also unlikely to observe or smell any chemical secretion under the given conditions, since some species, including Narceus americanus, might not have been capable of doing so as defense.
Limitations to this experiment slower or no response the probe since the millipedes we are using are probably used to human presence versus millipedes in the wild. Also, millipedes have very few natural predators, so they are not internally geared to fear anything. If we could go back and re-do the experiment, we would use a bird as a natural predator instead of a spider, and that would yield a more accurate measure of response because the millipede would actually coil.
Kime, R. Desmond. (2000). Trends in the ecological strategies and evolution of millipedes (Diplopoda). Biological Journal of the Linnean Society. : 333-349. Rowland, Shelley M. (June 2009). Millipedes. American Tarantula Society. Srinivasa, Y. Y., & Mohanraju, J. J. (2011). To Coil, or Not to – Activity Associated Ambiguity in Defense Responses of Millipedes. Journal Of Insect Behavior. pg. 24 (6), 488-496. doi:10.1007/s10905-011-9276-6