Pill Bug Lab

Light Intensity Effects on Taxis of Pill Bugs

By Laura Frechette, Brenna Frechette, Dara Manness, & Victoria Spencer

Introduction

In this experiment, we investigated:

• the natural animal behavior of pill bugs, specifically taxis.
• Taxis is a directed motion in response to a stimulus, and it implies an organism’s innate ability to sense the presence of a stimulus change.

Problem Statement

Does light intensity affect the Taxis of pill bugs?

http://outreach.mcb.harvard.edu/teachers/Summer05/ElizabethMick/PillbugBehavior.pdf

http://www.worldbookonline.com/student/article?id=ar753772&st=pill+bugs

http://science-ed.pnnl.gov/pals/resource/cards/pillbugs.stm

Hypothesis

If the pill bugs are presented with a choice of a lighter or darker environment, then they will move towards the side with the least light because they are naturally found in shaded areas

We decided to favor the pill bugs natural movement gravitating towards darker areas because though we knew they liked dark environments because they are typically found beneath rocks, through research we learned why these insects prefer to live in dimly lighted or dark habitats like underneath rocks, logs, boards, and leaves . They favor these dark areas because pill bugs are isopods (terrestrial crustaceans) related to aquatic crustaceans like crabs and crayfish. Because they are distantly related to these aquatic creatures, pill bugs are always in danger of drying out, so they avoid the light/stay out of the sun to prevent drying out . In fact, you can rarely see pill bug in the daytime because of their strong preferences for dark places; only at night do they venture from these hiding places to wander around . After discovering this information, we decided to test it out to see for ourselves which environment they would naturally move toward when presented with both a darker and lighter habitat option.

Materials and Methods

In this experiment, we set out to examine the natural behavior of pill bugs. These pill bugs are normally found in damp, dark locations. Therefore, we designed our experiment to see whether they exhibit taxis. Taxis is a specific, directed motion in response to a stimulus. It implies an innate sense of the stimulus, which in this case was light intensity.

• Our independent variable~ change in light intensity.
• 3 different degrees of light intensity. The first was no change at all.
• Control Group~ two joining petri dishes completely exposed to the natural light of the classroom.
• We conducted the experiment during the day in a brightly lit classroom. This represented the natural light.
• Next, we covered one of the petri dishes with parchment paper. This translucent paper allowed some light to pass through, but not all the natural light from the classroom. This created less light intensity.
• After this, we covered one petri dish with dark construction paper. This allowed for little to no light to pass through. Therefore, the light intensity would be closest to the pill bugs’ natural environment.
• After this, we did a trial with one petri dish covered in parchment paper and the other with the dark construction paper.
• Dependent Variable- The changes in light intensity affected the pill bugs behavior
• Our controls for this experiment:
• the dampness of the environment
• the time the pill bugs were given to move.
• We collected our data by counting the starting value of pills bug on each side of the petri dishes. Then, we changed the light intensity by covering one of the sides. After one minute, we counted the number of pill bugs on the uncovered side. Through deductive reasoning, we established the count of pill bugs on the other side. We repeated this after 3 minutes and then after 5 minutes. Once all the trials were completed, we had a great deal of quantitative data. We examined our data by placing the count of pill bugs on each side on a line graph. We could more clearly see the movement of pill bugs from one side to the other.

5+7=

(cc) image by anemoneprojectors on Flickr

This experiment investigates the natural behavior of pill bugs. We designed this experiment to test light intensity’s effect on the taxis, or directed motion in response to a stimulus, of the pill bugs. By joining two petri dishes, we created a chamber. In our trials, we covered half the chamber with parchment paper and black construction paper to decrease the light intensities. We found the pill bugs moved towards the sides with the decreased light intensity. This proved that pill bugs exhibit taxis towards decreased light intensities.

Results

Experimental Group 1

Experimental Group 2

Results of Pill Bug Lab

Control Group

Experimental Group 3

Abstract

Whitworth, Jeff. "Pill bug." World Book Student. World Book, 2012. Web. 17 Sept. 2012.

"Resource Cards." PNNL: Science & Engineering. N.p., n.d. Web. 17 Sept. 2012. <http://science-ed.pnnl.gov/pals/resource/cards/pillbugs.stm>.

Works Cited

Discussion

Our results were definitely consistent with our hypothesis stated earlier as in each trial, when presented with the choice, the pill bugs more or less moved to the darker of the two sides. We were already expecting this to occur since these insects favor a dark environment to shade themselves from the drying effects of sunlight, which the un-shaded petri dish represented. In the Control group with Natural Light vs. Natural Light, where both sides of the two petri dish chamber were uncovered, the number of bugs on either side stayed pretty much even, with only a one bug difference between the two at any point in time. Both sides overall had basically ten bugs each or a close nine to eleven bug ratio. In the Parchment Paper vs. Natural Light trial, the insects made a steady, natural movement to the slightly darker side provided by the cover of the translucent paper. Starting off with eleven insects on Side A (Parchment Paper) and nine in Side B (Natural Light), the number of bugs slowly began to climb in Side A, peaking at fifteen insects after the first two minutes. Because the parchment paper offers only a minuscule amount of coverage though, about two or three insects did not detect the difference in light intensity and returned to the Natural Light side, Side B, reducing Side A’s bug count to thirteen and then finally twelve after the six minutes of testing had elapsed. Overall, Side A housed the majority of the bugs throughout the six minutes, demonstrating how the bulk of the insects predominantly favored the slight shade created by the translucent parchment paper.

In the Black Paper vs. Natural Light trial, similar taxis occurred as the bugs gravitated towards the opaque darkness provided by the black paper and shied away from remaining in the uncovered, exposed side of the chamber. Starting off with six pill bugs in Side A (Black Paper) and 14 bugs in Side B (Parchment Paper), the insect gravitated once more the protective of the least light intense area of Side A. After two minutes, Side A hosted seven bugs to Side B’s thirteen. At the four minute checkpoint, Side A contained eight insects to Side B’s twelve. Then finally, after six minutes, Side A took the lead over Side B with a total of eleven bugs to nine.

Lastly, in the Black Paper vs. Parchment Paper trial, where both sides of the chamber were subject to some form of shade, the pill bugs displayed a preference for the darker black paper side than the lighter cover provided by the parchment paper. At the start, Side A, parchment paper, contained twelve insects while Side B, black paper, had only eight. At the two minute checkpoint, Side B began to increase its population, gaining one bug and totaling nine insects to Side A’s eleven. After four minutes though, the two sides were dead even with both Side A and Side B housing ten bugs each. At six minutes though, the tie was broken and the scales tipped in favor of the darker side, Side B containing eleven insects while Side A, the lighter side, contained only nine. This thus proved our hypothesis correct, in which if a pill bug is exposed to two different light intensities, it will always choose the darker of the two naturally and instinctively so that it may better shield itself from the sun and avoid dehydration. Through the experiment, our results have answered the problem we entered into this scientific endeavor uncertain of; does light intensity affect the taxis in pill bugs? Indeed light intensity does affect the specific, directed motion of these insects. With light concentration as our choice stimulus, the bugs reacted accordingly, moving towards the darker side of the two sided chamber.

In respect to validity issues, our results were overall valid except for the fact that when setting up our chambers, we had some exposed masking tape. When the bugs would come in contact with the tape they would become stuck and unable to move from one side to another. Also during the process of capturing the pill bugs and securely containing them within the double petri dish chamber, one or two of our insects died due to rough handling, possibly skewing our results. Finally, when we were counting the number of insects present on either side at each two minute checkpoint interval, there were instances where a couple of bugs would be halfway in one side and halfway in another, making it difficult to judge which side they were truly preferring or favoring. Despite these minor blemishes in our experiment though, we are confident in our experiment’s yield and believe that our results are as valid and dependable as we could humanly control.