Wednesday, December 3, 2008
Abstract
This experiment aims to study the food preference of earthworms. It was designed to see the effect of the presence of organic matter in relation to food preference. Bins were filled with both soil with organic matter and soil without organic matter in the same container. The organic matter consisted of newspaper clippings and grass clippings. Red wigglers (Eisenia foetida) were placed in the center and observed 48 hours later. Their preference was determined by the side of the bin where they were found. Repeated tests along with ph and nitrogen testing have provided a view into the behavior of earthworm food preference.
Introduction
Earthworms have been known for quite some time as being an integral part of ecosystems across the globe. They play an essential role in cycling nutrients essential to plant species in the soil they inhabit. There are also hundreds of species of animals whose diet consists of earthworms, sometimes almost exclusively (Curry 1998). Today it might seem obvious that earthworms play an important role in ecosystems, but it was Charles Darwin that brought the importance of them to the public (Edwards 1998).
Studies of earthworms have since given us a more complete view of animal behavior, ecology, and the history of the planet. A study conducted on islands, including newly formed volcanic islands has tested the hypothesis that earthworms cannot travel across salt water (James 1998). While we continue to study earthworms, we are continually learning more about their habitat and behavior.
There is much known about the factors affecting the presence of earthworms such as the presence of organic matter, soil texture, and moisture level. Earthworms prefer soils with a medium clay content; while it has been shown that earthworm activity as increased with an increase in moisture (Curry 1998).
This experiment is investigating food preference of the specific earthworm species, red wigglers (Eisenia foetida) in regards to organic matter content. We will use the data collected to determine if there is any preference. Our initial hypothesis is that red wigglers will prefer soil with an organic source over soil lacking an organic source. Also, we investigated a preference of organic material between newspaper and grass. Nitrogen and pH levels were measured to see if they could have an impact on food preference.
Studies of earthworms have since given us a more complete view of animal behavior, ecology, and the history of the planet. A study conducted on islands, including newly formed volcanic islands has tested the hypothesis that earthworms cannot travel across salt water (James 1998). While we continue to study earthworms, we are continually learning more about their habitat and behavior.
There is much known about the factors affecting the presence of earthworms such as the presence of organic matter, soil texture, and moisture level. Earthworms prefer soils with a medium clay content; while it has been shown that earthworm activity as increased with an increase in moisture (Curry 1998).
This experiment is investigating food preference of the specific earthworm species, red wigglers (Eisenia foetida) in regards to organic matter content. We will use the data collected to determine if there is any preference. Our initial hypothesis is that red wigglers will prefer soil with an organic source over soil lacking an organic source. Also, we investigated a preference of organic material between newspaper and grass. Nitrogen and pH levels were measured to see if they could have an impact on food preference.
Methods
We used a simple procedure to investigate the food preference of red wigglers, Eisenia foetida. First, we established that the worms would prefer soil that included organic matter over simple potting soil by setting up a bin where half of the area was potting soil while the other half was a potting soil/grass mixture. We placed ten worms on the dividing line between the two soil types, placed the container into a black plastic bag to prevent light penetration, and left the container undisturbed for 48 hours. We then checked the bin and found that all of the worms were located in the soil/grass mixture. This data supports our hypothesis that red wigglers have a soil preference, and thus we were able to begin our experiment.
The experiment consisted of 3 sets of 2 bins. Each bin had two different soil types on either half of the container. The sets of containers were combinations of the following:
1. A grass/soil mixture vs. potting soil
2. A newspaper/soil mixture vs. potting soil
3. A grass/soil mixture vs. a newspaper/soil mixture
The potting soil served as the control in this experiment. In order to control variables that could influence the soil preference of earthworms, the soil volume, texture, and moisture was kept constant for each trial. Each bin contained 225 grams of soil and 500mL of water. In the bins with a grass or newspaper soil mixture, 500 mL of either grass or newspaper was added and mixed throughout the soil. We placed 10 worms in the middle of each bin and covered the bins with a black plastic bag. We checked the bins 48 hours later and counted the worms in relation to their location. If a worm was found on the dividing line between two soil types, the worm was not recorded as having a preference for either soil. The location of the worm within the bin was used to determine food preference. This process was repeated twice to collect ample data to speculate on the food preference of red wigglers.
The pH and nitrogen levels of each soil type were also measured using a soil testing kit.
Testing the pH level of the soil.
Testing the nitrogen level of the soil.
The experiment consisted of 3 sets of 2 bins. Each bin had two different soil types on either half of the container. The sets of containers were combinations of the following:
1. A grass/soil mixture vs. potting soil
2. A newspaper/soil mixture vs. potting soil
3. A grass/soil mixture vs. a newspaper/soil mixture
The potting soil served as the control in this experiment. In order to control variables that could influence the soil preference of earthworms, the soil volume, texture, and moisture was kept constant for each trial. Each bin contained 225 grams of soil and 500mL of water. In the bins with a grass or newspaper soil mixture, 500 mL of either grass or newspaper was added and mixed throughout the soil. We placed 10 worms in the middle of each bin and covered the bins with a black plastic bag. We checked the bins 48 hours later and counted the worms in relation to their location. If a worm was found on the dividing line between two soil types, the worm was not recorded as having a preference for either soil. The location of the worm within the bin was used to determine food preference. This process was repeated twice to collect ample data to speculate on the food preference of red wigglers.
The pH and nitrogen levels of each soil type were also measured using a soil testing kit.
Testing the pH level of the soil.
Testing the nitrogen level of the soil.
Results
Careful interpretation of the data allows speculation to be made on our hypotheses. The total number of worms collected from each of the three trials can be viewed in Table 1, which also reveals the number of worms collected from each set of bins during all three trials. The totals were calculated by adding the number of worms found in the specified location of each bin. Figure 4 illustrates the overall location of worms collected in the experiment, showing that the greatest number of worms was found in the grass mixture soil. Also, worms preferred a soil with newspaper or grass over potting soil. To determine if these results were do to chemical factors of the soil, the pH and nitrogen levels were measured for each soil type (Table 5).
The results of this experiment support our first hypothesis and show that red wrigglers prefer soil with a source of organic matter over potting soil, which does not have a source of organic matter (Figure 1 and 2). Grass and newspaper served as our source of organic matter in this experiment. The conclusion that earthworms prefer soil with either grass or newspaper over potting soil is confirmed by two t-tests. This determines that these results are statistically significant due to a p-value of 0.0000029 and 0.006128 for experiments completed with grass and newspaper respectively (Tables 2 and 3). The differences between these data sets are statistically significant because the p-value is less than 0.05.
These results do not support our second hypothesis that red wrigglers will prefer a grass mixture soil over a newspaper mixture soil (Figure 3). A t-test reveals that the differences between the two data sets are not significant due to a p-value greater than 0.05 (Table 4). Therefore, the variation between the worms found in a grass mixture or a newspaper mixture is not statistically significant and does not support our hypothesis that red wigglers will prefer a grass mixture soil over a newspaper mixture soil.
Table 1. Totals of worm (Eisenia foetida) location in different conditions from three trial experiments.
Table 2. T-test assuming equal variances (potting soil vs. grass mixture)
Table 3. T-test assuming equal variances (potting soil vs. newspaper mixture)
Table 4. T-test assuming equal variances (grass mixture vs. newspaper mixture)
Table 5. Average pH and nitrogen levels of three soil types.
Figure 1. Total number of worms (Eisenia foetida) found in potting soil or grass mixture from containers with potting soil vs. grass mixture from each of three trials.
Figure 2. Total number of worms (Eisenia foetida) found in potting soil or newspaper mixture from containers with potting soil vs. newspaper mixture from each of three trials.
Figure 3. Total number of worms (Eisenia foetida) found in grass mixture soil or newspaper mixture soil from containers with grass/soil mixture vs. newspaper/soil mixture from each of three trials.
Figure 4. Total number of worms (Eisenia foetida) found in potting soil, grass, or newspaper in all containers from each of three trials. The final column is the sum of worms found in grass and newspaper during each trial of the experiment.
The results of this experiment support our first hypothesis and show that red wrigglers prefer soil with a source of organic matter over potting soil, which does not have a source of organic matter (Figure 1 and 2). Grass and newspaper served as our source of organic matter in this experiment. The conclusion that earthworms prefer soil with either grass or newspaper over potting soil is confirmed by two t-tests. This determines that these results are statistically significant due to a p-value of 0.0000029 and 0.006128 for experiments completed with grass and newspaper respectively (Tables 2 and 3). The differences between these data sets are statistically significant because the p-value is less than 0.05.
These results do not support our second hypothesis that red wrigglers will prefer a grass mixture soil over a newspaper mixture soil (Figure 3). A t-test reveals that the differences between the two data sets are not significant due to a p-value greater than 0.05 (Table 4). Therefore, the variation between the worms found in a grass mixture or a newspaper mixture is not statistically significant and does not support our hypothesis that red wigglers will prefer a grass mixture soil over a newspaper mixture soil.
Table 1. Totals of worm (Eisenia foetida) location in different conditions from three trial experiments.
Table 2. T-test assuming equal variances (potting soil vs. grass mixture)
Table 3. T-test assuming equal variances (potting soil vs. newspaper mixture)
Table 4. T-test assuming equal variances (grass mixture vs. newspaper mixture)
Table 5. Average pH and nitrogen levels of three soil types.
Figure 1. Total number of worms (Eisenia foetida) found in potting soil or grass mixture from containers with potting soil vs. grass mixture from each of three trials.
Figure 2. Total number of worms (Eisenia foetida) found in potting soil or newspaper mixture from containers with potting soil vs. newspaper mixture from each of three trials.
Figure 3. Total number of worms (Eisenia foetida) found in grass mixture soil or newspaper mixture soil from containers with grass/soil mixture vs. newspaper/soil mixture from each of three trials.
Figure 4. Total number of worms (Eisenia foetida) found in potting soil, grass, or newspaper in all containers from each of three trials. The final column is the sum of worms found in grass and newspaper during each trial of the experiment.
Discussion
This experiment served as a preliminary investigation to examine the food preferences of red wigglers, Eisenia foetida. Worms are an important component of the ecosystem because they break down organic wastes, which provide fertile soil for living plants. Therefore, these worms can be useful in composting bins in a process called vermicomposting (Dickerson 2004). Vermicomposting, or composting with worms, is a useful technique to recycle human food waste, yard waste, and paper products. Worm castings, which result from the digestion and secretion of organic material through the worm, create a nutrient rich soil that is ideal for plant growth. Worm castings often contain “5 to 11 times more nitrogen, phosphorus, and potassium than the surrounding soils” (Dickerson 2004). Therefore, using worms to decompose organic matter mutually benefits earthworms through providing a food source and plants, which benefit from their nutrient enhanced soil. By placing red wigglers into soils with different sources organic matter, we hoped to determine the food preference of red wigglers between grass clipping and newspaper clippings. This information may be useful when using earthworms as part of a composting bin because the proper ratios of organic matter could enhance the survival and reproduction of red wigglers, thus creating a more nutrient rich soil.
Our first hypothesis that red wigglers would prefer soil with organic matter over soil without organic matter was supported with data from our experiment (Figure 1 and 2). It was determined that red wigglers preferred soil with an organic source because a significant number of worms were found in the soil containing organic matter (grass or newspaper) compared to the soil containing potting soil, which lacked a source of organic material. Since worms rely on a source of organic matter to survive, these results were expected. In addition, these results also provide evidence that earthworms prefer soil with an organic source over soil without an organic source. From these results, we were able to test whether a red wiggler would prefer soil containing grass clippings over soil containing newspaper clippings.
By setting up bins with soils with two organic sources, where half the soil contained grass clippings and half the soil contained newspaper clippings, we were able to investigate the preference of red wrigglers. This was determined by their location in the bin after forty-eight hours. Since the difference between data sets of worms found in grass containing soil vs. newspaper containing soil showed no statistical significance, the hypothesis that worms would prefer grass containing soil over newspaper containing soil was not supported. From this data, it could be speculated that earthworms will simply exist in soil containing organic matter, regardless of its source.
However, prior investigations provide evidence that factors beyond organic matter influence the location of worms in soil. These factors include the soil’s moisture, texture, depth, pH, and nitrogen content (Curry 1998). This experiment controlled the variables of moisture, texture, and depth by keeping these factors constant for both soils containing grass or newspaper clippings. The pH and nitrogen content of soils containing grass vs. soils containing newspaper could differ between soils and thus influence the location of earthworms during the experiment. While differences exist between species, it has been determined that worms generally prefer soil with a pH in the range of 5.0-7.4 (Curry 1998). Our hypothesis that red wigglers would prefer grass clippings over newspaper clippings was based on the assumption that the dyes in newspaper could contribute to a more acidic soil, which could deter worms from choosing newspaper as a food source. However, the pH measured for each soil type was within the 6.0-7.0 range and therefore probably did not influence the location of worms in this experiment. The difference in nitrogen content between soil containing grass and soil containing newspaper was not large in each trial, so nitrogen levels also probably did not play a role in the worms’ location. Since the factors contributing to worm soil location were not significantly different between soil types and there was no significant difference of the number worms found in a specific soil, a preference for grass or newspaper as a food source was not evident in this experiment.
Extensions of this experiment can easily be completed to investigate the food preference of earthworms. For example, various organic sources could be tested by repeating the experiment and adding another organic source to the soil. Some examples could include fruit scraps, leaves, vegetable scraps, or manure. Measuring the preference of worms of each organic source would be useful to determine the ratio of organic matter to add to a composting bin. By creating a favorable environment for worms, the quality of soil can also be enhanced by facilitating to worm survival and reproduction. Also, the preference of organic texture can also be useful to creating a healthy environment for worms. It may be useful to finely chop waste so that worms can consume and digest organic materials more easily. Finally, different species of worms could be used to determine if they differ in food preference. Our experiment used red wigglers (Eisenia foetida), but another worm species may yield different results. Many extensions of this experiment could provide useful insight on the dietary and soil preferences of worms.
Using a simple procedure, we completed this preliminary experiment to determine the food preference of earthworms. While our data supports the hypothesis that earthworms will prefer soil with an organic source over soil lacking organic material, the data did not reveal a worm preference between soil containing grass or newspaper. There are a few modifications that could be made to improve this experiment. First, we used the same worms for each trial, which could contribute to the worm location during each trial. Perhaps using a new set of worms would result in different data. Also, if more trial were conducted, a greater amount of data collected could reveal trends in worm soil preference. Finally, a test of the soil’s pH and nitrogen content before and after the addition of worms could provide evidence of the worms’ efficiency to decompose the organic source.
Overall, this experiment provides evidence that earthworms decompose organic material found in soils. A preference between soil containing grass or newspaper was not determined during this experiment. This does not diminish the importance that worms, such as red wigglers, play in the ecological cycle by decomposing organic material. Humans can accelerate and exploit the decomposition process by using worms in composting bins, a process known as vermicomposting. More research would need to be completed to determine the optimal environment and food source for red wigglers. Regardless of a preference for a specific organic source, worms provide nutrient rich soils for plants through the decomposition of organic materials. Determining worm food preference would serve to accelerate decomposition and promote the health of worms to create an environment where both worms and plants can prosper.
Our first hypothesis that red wigglers would prefer soil with organic matter over soil without organic matter was supported with data from our experiment (Figure 1 and 2). It was determined that red wigglers preferred soil with an organic source because a significant number of worms were found in the soil containing organic matter (grass or newspaper) compared to the soil containing potting soil, which lacked a source of organic material. Since worms rely on a source of organic matter to survive, these results were expected. In addition, these results also provide evidence that earthworms prefer soil with an organic source over soil without an organic source. From these results, we were able to test whether a red wiggler would prefer soil containing grass clippings over soil containing newspaper clippings.
By setting up bins with soils with two organic sources, where half the soil contained grass clippings and half the soil contained newspaper clippings, we were able to investigate the preference of red wrigglers. This was determined by their location in the bin after forty-eight hours. Since the difference between data sets of worms found in grass containing soil vs. newspaper containing soil showed no statistical significance, the hypothesis that worms would prefer grass containing soil over newspaper containing soil was not supported. From this data, it could be speculated that earthworms will simply exist in soil containing organic matter, regardless of its source.
However, prior investigations provide evidence that factors beyond organic matter influence the location of worms in soil. These factors include the soil’s moisture, texture, depth, pH, and nitrogen content (Curry 1998). This experiment controlled the variables of moisture, texture, and depth by keeping these factors constant for both soils containing grass or newspaper clippings. The pH and nitrogen content of soils containing grass vs. soils containing newspaper could differ between soils and thus influence the location of earthworms during the experiment. While differences exist between species, it has been determined that worms generally prefer soil with a pH in the range of 5.0-7.4 (Curry 1998). Our hypothesis that red wigglers would prefer grass clippings over newspaper clippings was based on the assumption that the dyes in newspaper could contribute to a more acidic soil, which could deter worms from choosing newspaper as a food source. However, the pH measured for each soil type was within the 6.0-7.0 range and therefore probably did not influence the location of worms in this experiment. The difference in nitrogen content between soil containing grass and soil containing newspaper was not large in each trial, so nitrogen levels also probably did not play a role in the worms’ location. Since the factors contributing to worm soil location were not significantly different between soil types and there was no significant difference of the number worms found in a specific soil, a preference for grass or newspaper as a food source was not evident in this experiment.
Extensions of this experiment can easily be completed to investigate the food preference of earthworms. For example, various organic sources could be tested by repeating the experiment and adding another organic source to the soil. Some examples could include fruit scraps, leaves, vegetable scraps, or manure. Measuring the preference of worms of each organic source would be useful to determine the ratio of organic matter to add to a composting bin. By creating a favorable environment for worms, the quality of soil can also be enhanced by facilitating to worm survival and reproduction. Also, the preference of organic texture can also be useful to creating a healthy environment for worms. It may be useful to finely chop waste so that worms can consume and digest organic materials more easily. Finally, different species of worms could be used to determine if they differ in food preference. Our experiment used red wigglers (Eisenia foetida), but another worm species may yield different results. Many extensions of this experiment could provide useful insight on the dietary and soil preferences of worms.
Using a simple procedure, we completed this preliminary experiment to determine the food preference of earthworms. While our data supports the hypothesis that earthworms will prefer soil with an organic source over soil lacking organic material, the data did not reveal a worm preference between soil containing grass or newspaper. There are a few modifications that could be made to improve this experiment. First, we used the same worms for each trial, which could contribute to the worm location during each trial. Perhaps using a new set of worms would result in different data. Also, if more trial were conducted, a greater amount of data collected could reveal trends in worm soil preference. Finally, a test of the soil’s pH and nitrogen content before and after the addition of worms could provide evidence of the worms’ efficiency to decompose the organic source.
Overall, this experiment provides evidence that earthworms decompose organic material found in soils. A preference between soil containing grass or newspaper was not determined during this experiment. This does not diminish the importance that worms, such as red wigglers, play in the ecological cycle by decomposing organic material. Humans can accelerate and exploit the decomposition process by using worms in composting bins, a process known as vermicomposting. More research would need to be completed to determine the optimal environment and food source for red wigglers. Regardless of a preference for a specific organic source, worms provide nutrient rich soils for plants through the decomposition of organic materials. Determining worm food preference would serve to accelerate decomposition and promote the health of worms to create an environment where both worms and plants can prosper.
References
Cooperative Extension Services: College of Agriculture and Home Economics. (2001). Vermicomposting (1st ed.). La Cruces: George Dickerson.
Curry, J.P. (1998). Factors Affecting Earthworm Abundance in Soils. In Edwards, Clive A (Ed.), Earthworm Ecology (37-64). Boca Raton: CRC Press LLC.
Edward, C.A. (1998). Preface. In Edwards, Clive A (Ed.), Earthworm Ecology (v-vi). Boca Raton: CRC Press LLC.
James, S. (1998). Earthworms and Earth History. In Edwards, Clive A (Ed.), Earthworm Ecology (3-12). Boca Raton: CRC Press LLC.
Curry, J.P. (1998). Factors Affecting Earthworm Abundance in Soils. In Edwards, Clive A (Ed.), Earthworm Ecology (37-64). Boca Raton: CRC Press LLC.
Edward, C.A. (1998). Preface. In Edwards, Clive A (Ed.), Earthworm Ecology (v-vi). Boca Raton: CRC Press LLC.
James, S. (1998). Earthworms and Earth History. In Edwards, Clive A (Ed.), Earthworm Ecology (3-12). Boca Raton: CRC Press LLC.
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