Do Pillbugs Prefer A Light or Dark Environment?
BY: Joe Brown
Lab Partners: Mary Smith, Susie Que
Honors Biology
Class B
Mrs. West
March 31, 2006
ABSTRACT:
This experiment tested whether pillbugs preferred a light or dark environment.
It was predicted that the pillbugs would prefer a dark environment, as this is
where they tend to be found in nature. A comparison study was set up using 8
pillbugs in a closed tray, covering half of the tray with construction paper to
create a dark area and light area of equal size on the tray.
The number of
pillbugs in each area of the tray was recorded every minute for ten consecutive
minutes. Pillbugs were two times more likely to be in the dark area as the light
area.
PURPOSE:
The reason for doing this experiment was to determine whether pillbugs
preferred a light or dark environment.
Pillbugs, also known as sowbugs, or woodlice, are familiar backyard creepy
crawlies to most of us. Pillbugs are correctly classified as terrestrial Isopods, and
belong to the Class Crustacea. Pillbugs can be searched for in any sites that
provide locally humid retreats during the day. Compost piles and leaf litter
frequently have rich populations, and large numbers can often be found beneath
logs and among rubble piles. All species are nocturnal and may venture over
considerable distances during the night. On humid evenings, they can often be
seen in large numbers with the help of a flashlight. Pillbugs feed on dead
vegetation, such as wood and leaf litter.
Pillbugs live outside are able to get the necessary amount energy from organic
matter by living outside, where water and organic matter is plentiful. They can,
however, be found indoors in dark, damp places, such as basements or
houseplants. Living in moist places is important for pillbugs so they can take in
enough water, and if water is not available, they group together to prevent water
loss
Pillbugs most often live in dark places because they have a negative
phototaxis. Darker places also tend to be cooler and damper, which could be
another reason pillbugs prefer darkness Pillbugs probably prefer the darkness
because dark environments are moister, so therefore, they are able to take in
more water to keep up with their rapid diffusion of gases for respiration.
(McKenzie, 1999).
The hypothesis is that if pillbugs are given a choice of a light or dark
environment, then they will prefer the dark environment.
MATERIALS:
8 pillbugs
1 piece of construction paper
1 enclosed tray
scotch tape
stop watch or watch with second hand
PROCEDURE:
1.) A tray was obtained and half of the top of the tray was covered with
construction paper by taping the construction paper to the tray.
2.) Eight pillbugs were placed in the tray and allowed to acclimate to the
environment for ten minutes. See Figure 1.
Figure 1.
3.) After ten minutes, data was collected as to the area (light or dark) the pillbugs
were in every consecutive minute for ten minutes. Data was recorded in Table 1.
4.) Pillbugs were returned to their original container as directed by the instructor.
In this lab, the independent variable was the amount of light, the dependent
variable was where the pillbugs went, and the control was the area with light.
RESULTS:
Table 1. Number of Pillbugs in lighted and darkened area over time
Minutes after Starting
1
2
3
4
5
6
7
8
9
10
Avg
Pillbugs in the Lighted
Area
2
1
1
2
4
3
4
2
3
4
2.6
Pillbugs in the Darkened
Area
6
7
7
6
4
5
4
6
5
4
5.4
Graph: (see attached)
CONCLUSION:
In this lab, the pillbugs were allowed to acclimate to their environment for ten
minutes before collecting data.
Collecting the data for each minute over ten
minutes allowed data to be gathered from many trials, which improved
experimental validity.
The results obtained in this lab support the hypothesis
that the pillbugs would prefer a darkened environment, as approximately twice as
many pillbugs on average were found in the dark side of the tray as on the
lighted side of the tray.
The pillbugs tended to crawl on each other, on the construction paper, and made
efforts to get out of the tray, which led to uncertain information in the data, as
several times the pillbugs were poked back into the tray. These attempts to
escape might have led to an unnatural preference for the pillbugs for the lighted
side of the tray, where the escape route could be found. The pillbugs also
crawled on top of each other, which may have skewed the data as well.
The
pillbugs provided in this experiment were of different sizes. It is possible that
different sized pillbugs prefer different environments in reference to the amount
of light provided.
It is uncertain as to how this last observation might have
skewed the data.
This could be a subject for further experimental study.
Other factors, which may have skewed the data, would be the gender, age, and
general health of the pillbugs.
A perfectly controlled laboratory setup would
assure that these factors were completely the same in all the specimens.
(Michael Smith, 1996)
The lab could be modified to improve the results if more pillbugs of similar size
had been provided. Choice trays with higher, slipperier sides to prevent the
pillbugs from escaping would have been helpful as well.
Allowing more time for
data collection, as well as having more pillbugs would have provided for more
experimental trials, which would have led to more acceptable and valid results.
BIBLIOGRAPHY:
Buckley, James (2002). Organization and Analysis of Data. RegentsPrep.
http://home.oswego.org/staff/jbuckley/RegentsPrep/laboratory/organization.cfm
McKenzie, Greg (1999). Woodlice Online. Geocites.
http://www.geocities.com/CapeCanaveral/Hangar/7649/woodlice/habitat.htm
Smith, Dr. Michael J (1996). Designing Investigations with Pillbugs.
University of Delaware. http://www.udel.edu/msmith/pillbugs.html
http://www.northern.edu/natsource/INVERT1/Pillbu1.htm