The organism used in this experiment is Armadillidium vulgare which is commonly called a pillbug, sowbug, or roly-poly. The pillbug belongs to the Kingdom Animalia, Phylum Arthropoda, Class Crustacea, and Order Isopoda. To understand this experiment it is important to have some knowledge of the organism being observed. The pillbug is an isopod. The pillbug is made up of three body parts. They are the head, thorax, and abdomen. This organism has two pairs of antennae (one prominent and one inconspicuous), simple eyes, seven pairs of legs, seven separate segments on the thorax, and paired appendages at the end of the abdomen called uropods. The color varies from dark gray to white with pattern or white without pattern. Male and female pillbugs differ in that a female has leaf-like growths at the base of some of its legs. The purpose of these pouches is to hold developing eggs and embryos. Males differ in that the first two appendages on their abdomens are elongated copulatory organs. The immature isopod looks like an adult, save for its size, proportion, color, and sexual development. The pillbug is of the Order Isopoda. Isopods feed on dead or decaying plants or animals. Some isopods may eat living plants. They breathe with gills, and therefore their habitats are places of high humidity. During the day, pillbugs hide in moist places, such as under stone and bark. The organism being observed reproduces on land instead of in water. The eggs develop in a brood pouch filled with fluid. This organism produces between one and two broods. This depends upon the female’s size and condition. The female may stop growing under stress. This decreases the likelihood of reproducing more than once. The pillbug society is patriarchal. The burrow in which a pillbug family lives is guarded by the father. Both the father and mother gather the food. The entire pillbug family cleans the burrow. The young set out in February to create families of their own. Pillbugs are known for their defense mechanism of curling up into a tight ball.
As for the impact of isopods’ impact on the ecosystem, there are both positive and negative effects. Isopods cause minimal soil improvement and provide a food source for other animals. Large populations of isopods can eat and cause damage to plants. The role of the pillbug in the ecosystem is breaking down dead plants and animals. Pillbugs that live in gardens help the circulation of soil, but it’s possible they will eat small plants as they germinate. Overall, pillbugs have a small impact on the ecosystem.
To understand this experiment it is also important to be somewhat knowledgable on ethology, the study of animal behavior. Behavior is defined as an animal’s response to sensory input. There are two categories that a behavior can fall into. They are learned and innate. The behavior that places an animal in its favorite environment is called an orientation behavior. When an animal moves toward or away from a stimulus, it has exhibited taxis. Light, heat, moisture, sound, or chemicals are often the stimuli that cause taxis. Random movement that does not result in orientation with respect to a stimulus is known as kinesis. Another type of behavior is Agnostic behavior. This is exhibited when animals respond to one another by aggressive or submissive responses.
The pH of soil varies depending on the soil’s condition. There are plants that grow best when the soil is acidic, and there are some plants that grow best when the soil is basic. Most plants, however, show the best growth in areas where the pH ranges from 6.5 to 7.2, 7 being neutral. Hydrochloric acid and Sodium Hydroxide have pHs at the extremes of the pH scale. The pH of Hydrochloric acid, HCL, (0.1 M) is about 1.1. Sodium Hydroxide, KOH, (0.1 M) has a pH of about 13.5. Detritus is what isopods feed on, and it as a more acidic pH. When organic matter decays, H ions are produced. Therefore, acid is added to the soil. Generally, the acidity limit for plants is no lower than approximately 4.5 to 5.6 on the pH scale. The vapor pressure of a liquid refers to the idea that, in a closed container, evaporation will continue until equilibrium is reached. The vapor pressure of HCl and water are approximately equal (20 mmHg at room temperature, 22 C), and the vapor pressure of KOH for a 45% solution is approximately 2 mmHg.
The purpose of this experiment was to use pillbugs to examine animal behaviors and habitat preferences and to determine whether this organism prefers moist or dry habitats, dark or light habitats, and acidic or caustic environments With knowledge of isopods and pillbugs, it was hypothesized that the pillbugs would spend more time near the damp filter paper because of their need for high humidity in order to breathe. Given that pillbugs live under rocks and feed on decaying organisms, which release acid into the soil, it was also hypothesized that they would prefer the dark rather than light conditions and the acidic over the caustic environment.
Materials and Methods
Water
Pipet
Filter Paper (2 pieces)
Choice Chamber
Scissors
Soft Brush
10 Pill Bugs
Stopwatch
To observe pill bugs and their preference moist versus dry conditions, a choice chamber, consisting of two petri dishes connected to one another, was obtained and lined with filter paper. Two pieces of filter paper were cut to fit the chambers. One was then moistened, using a pipette, with a few drops of water. The second piece of circular filter paper was left dry. The moistened filter paper was placed at the bottom of one chamber, chamber 1, and the dry filter paper was placed at the bottom of the other, chamber 2. Then, using a soft brush, ten pill bugs were obtained from the stock of pill bugs, and then placed into the chambers. Also using a soft brush, five pill bugs were placed in the dry chamber while the remaining five were placed in the moist chamber and the chambers were closed. This pillbug count for each chamber was then recorded for time zero minutes. Using the stopwatch to track time, the count of pill bugs on each side of the choice chamber was then recorded every 30 seconds for ten minutes, and continued even when some may no longer have been moving or were all on one side. Notes were taken on the actions and interactions of the pill bugs throughout the ten minute period. Once ten minutes had elapsed, the pill bugs were returned to the stock culture.
Black Paper
White Filter Paper
Choice Chamber
10 Pill Bugs
Soft Brush
Scissors
Stopwatch
To determine the preference of pill bugs between light and dark habitats and conditions, a choice chamber with two connecting petri dishes was lined with two different types of paper. One piece of normal filter paper and one piece of black paper were both cut to fit the chambers. Next, the bottom of the inside of one dish, chamber 1, was covered with the unaltered, white filter paper and the other dish, chamber 2, was lined with the black paper. Then, using a soft brush, ten pill bugs were obtained from the pill bug stock culture, five of which were placed in the black-paper lined chamber and the remaining five were placed in the white paper lined chamber. The choice chamber was then closed. The initial pill bug count, 5 in each chamber was then recorded in the table. For a period of ten minutes, using a stopwatch to track time, the count of the pill bugs on each side of the choice chamber was recorded every thirty seconds. In addition, notes about the interactions of the pill bugs were taken throughout the ten minute period. The count continued to be taken, regardless of the lack of movement from the pill bugs or the concentration of all ten in one chamber. After the ten minutes had elapsed, the pill bugs were returned to the stock culture.
White Filter Paper (2 pieces)
0.1 M HCl (Hydrochloric Acid)
0.1 M KOH (Potassium Hydroxide)
Pipettes (1 or 2)
Filter Paper (3 Pieces)
3 – Choice Chamber
10 Pill Bugs
Scissors
Stopwatch
To determine and see the preference of pill bugs in terms of basic and acidic conditions, a 3-choice chamber was set up. Three pieces of filter paper were cut to fit the chambers. Using a pipette, about four drops of 0.1 M HCl were placed in a circular pattern about the paper. Another piece of filter paper was sprinkled with 0.1 M KOH in the same manner as was done with the hydrochloric acid. The HCl and KOH were applied to the filter paper in such a way that the paper was not drenched in the chemical. One chamber, the one connected to two other chambers was lined with an unaltered piece of filter paper. One of the two remaining chambers, chamber 1, was lined at the bottom (inside bottom) with the acidic filter paper and the remaining chamber, chamber 3, was lined at the bottom with the basic filter paper. Using a soft brush, the ten pill bugs were all removed from the stock culture and placed in chamber 2, the middle chamber consisting of the unaltered paper. The chambers were then covered and the pill bug count was recorded in the table for the initial time of 0 minutes. For the next ten minutes, the count of pill bugs in each of the three chambers was recorded every thirty minutes. The data continued to be collected even when they were no longer moving sides or were all on one side. After the ten minutes had elapsed, the ten pill bugs were returned to the stock culture.
Results
Table 1: Number of Pillbugs in Wet vs. Dry Chambers at Various Times
Time
(min.)
Number in Wet Chamber
Number in Dry Chamber
Other Notes
0
5
5
Begin moving instantly
0.5
2
8
Large number shifts together to one side
1
1
9
One more baby follows
1.5
3
7
Fighting between two larger isopods
2
5
5
Even out again
2.5
5
5
Move about but come back to even; one not moving
3
6
4
More to wet chamber
3.5
4
6
Back to Dry Chamber
4
5
5
Crawling on underside of paper
4.5
4
6
Fighting to get from one side to another
5
3
7
Large pillbug still not moving
5.5
6
4
Other pillbugs begin gathering around non-moving pillbug
6
7
3
Pillbugs piled on top of one another
6.5
5
5
Pillbug begins to move again
7
4
6
More to Dry Chamber
7.5
5
5
Back at even
8
6
4
Continual switch from chamber to chamber
8.5
7
3
Begin gathering at wet chamber
9
9
1
More join wet chamber
9.5
7
3
Crowded, a few go to dry chamber
10
9
1
Return to wet chamber
Table 2: Number of Pillbugs in Lighter vs. Darker Colored Chambers at Various Times
Time
(min.)
Number in Light
Chamber
Number in Dark Chamber
Other Notes
0
5
5
Begin moving instantly
0.5
3
7
Move to dark side
1
2
8
More to dark side
1.5
2
8
Remain, no overall movement
2
2
8
No overall movement
2.5
3
7
Begin going to white side
3
3
7
No overall movement
3.5
4
6
Moving to lighter side
4
2
8
Move to dark side
4.5
5
5
Equalize again
5
3
7
Fighting to get to dark side
5.5
5
5
Equalize again
6
4
6
More to Dark side
6.5
7
3
Piling up to get to lighter side
7
7
3
No overall movement
7.5
8
2
More in lighter side
8
9
1
More in lighter side
8.5
7
3
Move to dark side
9
5
5
Equalize again
9.5
3
7
Move to darker side
10
4
6
Young follows adult to other side
Table 3: Number of Pillbugs in Neutral, Acidic and Basic Chambers at Various Times
Time
(min.)
Number in Neutral Chamber (Control)
Number in Acidic Chamber
Number in Basic Chamber
Other Notes
0
10
0
0
Immediate Movement
0.5
2
5
3
Move to acidic
1
3
5
2
Stay around outside of chamber
1.5
6
2
2
Quickly out of acidic and into neutral area
2
4
3
3
More to basic area
2.5
5
2
3
Away from acidic area
3
2
3
5
More slowly moving to basic area
3.5
2
1
7
Movement to basic chamber
4
4
0
6
Pillbugs all out of Acidic area
4.5
1
1
8
Most in Basic area
5
1
4
5
Some return to acidic chamber
5.5
3
1
6
Slowly moving out of Acidic chamber and into neutral and basic chambers
6
4
1
5
Out of basic and into neutral
6.5
3
1
6
Back into basic area, around outside of filter paper
7
3
1
6
No overall movement
7.5
4
0
6
All gone from acidic area
8
3
0
7
More to basic area
8.5
4
0
6
Small shift
9
3
0
7
Reverse of shift
9.5
2
0
8
More to basic area more slowly than before test
10
1
0
9
More to basic area
Figure 1: Fluctuation in Number of Pillbugs in Wet and Dry Chambers
Figure 2: Fluctuation in Number of Pillbugs in Lighter and Darker – Colored Chambers
Figure 3: Fluctuation in Number of Pillbugs in Acidic, Neutral and Basic Chambers
Discussion
Table 4: Average Number of Pillbugs in Wet vs. in Dry Chambers
Time
(min.)
Number in Wet Chamber
Number in Dry Chamber
Average # of Pill Bugs in Wet
Average # of Pill Bugs in Dry
0
5
5
0.5
2
8
1
1
9
1.5
3
7
2
5
5
2.5
5
5
3
6
4
3.5
4
6
4
5
5
4.5
4
6
5
3
7
5.5
6
4
6
7
3
6.5
5
5
7
4
6
7.5
5
5
8
6
4
8.5
7
3
9
9
1
9.5
7
3
10
9
1
Total # of Pill bugs
108
102
5.143
4.857
Table 5: Average Number of Pillbugs in Lighter vs. Darker-Colored Chambers
Time
(min.)
Number in Light
Chamber
Number in Dark Chamber
Average # of Pill Bugs in White (Light)
Average # of Pill Bugs in Dark
0
5
5
0.5
3
7
1
2
8
1.5
2
8
2
2
8
2.5
3
7
3
3
7
3.5
4
6
4
2
8
4.5
5
5
5
3
7
5.5
5
5
6
4
6
6.5
7
3
7
7
3
7.5
8
2
8
9
1
8.5
7
3
9
5
5
9.5
3
7
10
4
6
Total # of Pill Bugs
93
117
4.429
5.571
Table 6: Average Number of Pillbugs in Neutral, Acidic and Basic Chambers
Time
(min.)
Number in Neutral
Chamber
Number in Acidic Chamber
Number in Basic Chamber
Average # of Pill Bugs in Neutral Chamber
Average # of Pill Bugs in Acidic Chamber
Average # of Pill Bugs in Basic Chamber
0
10
0
0
0.5
2
5
3
1
3
5
2
1.5
6
2
2
2
4
3
3
2.5
5
2
3
3
2
3
5
3.5
2
1
7
4
4
0
6
4.5
1
1
8
5
1
4
5
5.5
3
1
6
6
4
1
5
6.5
3
1
6
7
3
1
6
7.5
4
0
6
8
3
0
7
8.5
4
0
6
9
3
0
7
9.5
2
0
8
10
1
0
9
Total # of Pill Bugs
70
30
110
3.33
1.429
5.238
Figure 4: Comparison of Average Number of Pillbugs in Wet Chamber vs. in Dry Chamber
Figure 5: Comparison of Average Number of Pillbugs in Lighter-colored and Dark-colored Paper
Figure 6: Comparison of Average Number of Pillbugs in Acidic, Neutral and Basic Chambers
It was hypothesized that the pillbugs, given that they possess gills for respiration, and that they live where there is not a lot of light (under rocks and logs), they would prefer the damp chamber over the dry chamber and the dark chamber over the light chamber. Knowing that pillbugs feed off of decaying organic material, and the process of decay increases the soil acidity, it was hypothesized that the pillbugs would prefer the acidic chamber (the one with HCl), over the caustic (with KOH) and neutral chambers. The data collected supports the hypothesis. The mean number of pill bugs in each chamber was calculated by totaling the pillbug count for all twenty-one times in one chamber and then doing the same for the next chamber and then dividing the two totals by the total number of pillbugs counted. This number was 210 in each case. As evidenced by Table 4 and Figure 4, the mean number of pillbugs in the damp chamber over ten minutes was approximately 5.143, and the mean number of pillbugs in the dry chamber over ten minutes was approximately 4.857. The higher average of the damp chamber over the dry chamber shows taxis toward the stimulus (moisture).
The data collected also supported the second part of what was hypothesized. The mean number of pillbugs in the chamber with light paper was about 4.429. Table 5 and Figure 5 show the mean number of pillbugs in the dark chamber to be about 5.571. The results and the known habitats of pillbugs are consistent with one another.
The data collected in part three of the experiment did not support what was hypothesized. Table 6 and Figure 6 show that the basic environment (one with drops of KOH) was actually preferred over a neutral environment and the acidic environment (one with drops of HCl) by the pillbugs. The mean number of pillbugs in the neutral environment was about 3.33, for the acidic environment the mean was about 1.429 and for the caustic environment the mean was about 5.238. It’s possible the explanation for these results is the vapor pressure of the Hydrochloric acid being higher than that of the Sodium Hydroxide. Irritation caused by HCL vaporizing quickly and getting into the pillbugs’ gills would explain the lack of time spent in the chamber with the HCl on the filter paper. The lack of moisture on the plain filter paper could explain the lack of time spent in the neutral chamber. The pillbugs’ antennae would sense any chemical or something like it, and they would be attracted to that chamber. Agnostic behavior was exhibited by the pillbugs inside the choice chambers. Fighting between the pillbugs represents agnostic behavior. The results of the experiment would not be affected by errors in counting or other human errors.
The data collected from the experiment supported two thirds of what was hypothesized. The pillbugs’ preferences for dark and damp environments over light and dry environments were supported by the results. However, the results suggest that pillbugs preference is for the more caustic environments over the environments that are neutral or acidic.
Citations
1. Brown, Courtney Jane. “ADW: Armadillidium Vulgare: Information.” Animal Diversity Web. Web. 24 Mar. 2011. .
2. Lab # 11 Animal Behavior (College Board, 2001) AP® Biology Lab Manual for Students (2001) New Jersey: College Board. p. 125-131.
3. “Isopod, Pillbug, Sow Bug Information.” UA Center for Insect Science Education Outreach. Web. 24 Mar. 2011. .
4. “Soil PH and Soil Acidity or Alkalinity.” Landscaping and Lawns by Donnan Landscape. Web. 24 Mar. 2011. .
5. “HYDROCHLORIC ACID (LESS THAN 10%).” New Mallinckrodt Baker Website. Web. 24 Mar. 2011. .
6. “What Is Acidic Soil?” Web. 24 Mar. 2011. .
7. “Vapor Pressure.” Test Page for Apache Installation. Web. 24 Mar. 2011.
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8. “The MSDS HyperGlossary: Vapor Pressure.” Transferring You to the ILPI Home Page… Web. 24 Mar. 2011. .