Question

Introduction:

Pill bugs

In today’s exercise, we will be using the scientific method to study the behavior of the pill bug - Armadilidium vulgare. Pill bugs are also called woodlice and roly-poly bugs. They aren’t actually insects but belong to the subphylum Crustacea which means that they are more closely related to shrimp and lobsters.

Pill bugs are found in a variety of habitats including forests, grasslands, and urban areas. They prefer dark, moist areas and are often found under rocks, logs, and dead leaves. They feed on decaying organic matter such as rotting plant material as well as some living plants. They are considered a pest in the garden when they eat the tender shoots of young plants. Their natural predators include frogs, toads, lizards, and small mammals. Pill bugs are covered by a tough exoskeleton and will protect themselves by rolling into a ball.

Pill bugs have three basic body parts which are the head, thorax, and abdomen (Fig. 11.2). They have seven pairs of legs along the thorax and abdomen. Pill bugs have a large pair of antennae at the top of their head which is used to feel objects. The second pair of smaller, vestigial (remnant) antennae, as well as the eyes, are also found on the head. A pair of uropods are found at the posterior end of the animal and these appendages wick up water and act as rear antennae. Only the terminal end of the uropod, called the exopod, is visible when viewing the pill bug from its top side. Pill bugs exchange gases through their gills which are located on the underside.

Taxis

Taxis is an innate animal behavior observed as a movement of the animal. Positive taxis is a movement toward a stimulus and negative taxis is a movement away from a stimulus. We will be able to observe two types of taxis in pill bugs in today’s lab exercise. Phototaxis is movement in response to light. Animals exhibiting positive phototaxis will move toward light and those exhibiting negative phototaxis will move away from light. Chemotaxis is a response to chemicals as demonstrated by animals moving toward water and nutrients and away from toxins.

Part I – Background Research and Designing the Positive Control

1. Conduct background research by reading the introduction and other sources of information about pill bugs. Discover their preferred environmental conditions and food sources of pill bugs.

2. Write down this information under Background Research in the lab report.

3. We will be comparing the data from the different groups so we need to determine what environment we will use as our positive control.

4. Examine the materials available and discuss which materials the pill bugs should be attracted to in their natural environment. Select two materials that all groups will use in their positive control well.

5. Enter the positive control conditions in the lab Report.

Part II – Observations.

Materials:

4 pill bugs – obtain from instructor                           Stopwatch

Behavior tray                                                                     Ruler

Silver permanent marker

Procedure:

1. Put on your goggles and gloves and obtain four pill bugs from your instructor.

2. Take note of the distinguishing features of each pill bug. If you have trouble telling any of the pill bugs apart, mark them with the silver marker.

3. Assign a name to each pill bug and place it in the behavior tray.

4. Identify the body parts from Figure 11.1.

5. Observe the pill bugs for at least 15 minutes. Take note of the following:

a. How quickly the pill bug moves across 6 cm of ruler.

b. What triggers the pill bugs to roll into a ball (DO NOT HARM THE PILL BUG!).

c. How the pill bug interacts with other pill bugs.

d. Make note of any other observations regarding this pill bug.

6. Record your observations Table 1 in the Lab Report.

Part III – Formulating Hypotheses.

Materials:

4 pill bugs

Variety of test substances such as sand, coffee creamer, orange juice.

Procedure:

1. Examine the materials available for testing at your bench and the supply benches. The behavior tray has a central well for placement of the animals at the beginning of the experiment. The positive control materials should be placed in one of the four outer wells.

2. Select three different materials to use for your experimental conditions and place each in one of the remaining three wells of the behavior tray.

3. Use the information you have learned about the pill pugs to predict how the how the pill bugs will respond the substances/conditions you chose.

4. Develop a hypothesis for each substance/condition. Phrase each hypothesis in the form of an if-then statement. For example: “If the pill bug is exposed to a slice of apple it will move toward it.”

5. Enter your hypotheses in Table 2 of the Lab Report.

6. Write down the reasoning you used to develop your hypothesis.

Part IV – Data Collection

Procedure:

1. Place the control materials in one of the four outer wells.

2. Place the experimental materials in the remaining three outer wells (one material per well).

3. Place your four pill bugs in the center well. Start the timer.

4. At the end of one minute, enter the names of the pill bugs in each well in Table 3 of the Lab Report.

5. Repeat Step 4 every minute until the experiment has run for 15 minutes.

6. Determine if the pill bugs exhibited positive or negative taxis using the following criteria:

Positive taxis = Two or more pill bugs entered the well and remained in the well for at least two-time points (two minutes) in a row during the course of the 15 minutes..

Negative taxis = Less than two pill bugs entered the well and/or remained in the well for less than two-time points (two minutes) in a row in the course of the 15 minutes.

7. Enter your data (positive or negative taxis) into Table 4 and add the data to the chart on the board.

8. Enter the class data into Table 5 of the Lab Report. Use the class data for the same experimental materials you tested to complete the table in the results section of the Lab Report.

Lab Report Pill bug Behavior

Results:

Part IV. Data Collection

Contents of Well #1 _______________________

Contents of Well #2 _______________________

Contents of Well #3 _______________________

Contents of Well #4 _______________________

Table 3. Your group’s data

Time	Names of pill bugs in Well #1	Names of pill bugs in Well #2	Names of pill bugs in Well #3	Names of pill bugs in Well #4
1 minute
2 minutes
3 minutes
4 minutes
5 minutes
6 minutes
7 minutes
8 minutes
9 minutes
10 minutes
11 minutes
12 minutes
13 minutes
14 minutes
15 minutes

Table 4 - Taxis response to each substance for your pill bugs

Substance/Condition	Taxis response	Was your hypothesis supported? (Yes or no)
1.
2.
3.
4.

Conclusions (answer in complete sentences):

1. Why is it important to include positive control in your experiment?

2. Was the taxis response to your control what you expected? Explain.

3. Which (if any) experimental materials that supported your hypotheses?

4. Which (if any) experimental materials that did not support your hypotheses

5. If any of your results did not support your hypotheses provide possible explanations below:

6. Did any of the class results differ from your own?

7. Why might some pill bugs behave differently than others when exposed to the same substances/conditions?

Answer 1

1. Positive control is essential to establish comparison between the results obtained from the experiment deploying new methods and result obtained from a known method. A positive control is basically a control group that receives treatment other than the experimental treatment in order to produce expected effect.

2. Yes. The response of pill bugs depends on its sensitivity to the photons and chemicals to which it is exposed for observing their taxis. The taxis responses for the positive control group will be as per the desired response because it has been given a well-established treatment (other than experimental treatment) in order to produce a desired result. Like positive control there is a negative control group too, which is not exposed to any treatment. Hence the results of positive and negative control group will be as per the expectation of the researcher.

3. Test substances such as sand, coffee creamer, orange juice helped in supporting the hypothesis

4. Materials such as pill bugs , Stopwatch, Behavior tray, Ruler and Silver permanent marker did not supported the hypothesis directly but helped in making observation for testing the hypothesis