Spiders: An Organism for Teaching Biology

Introduction:
Spiders prey upon insects. Do they keep insect numbers down? What do we need to know in order to answer this question? A "Mark and Recapture" study is one method scientists use to estimate the number of individuals in a population when it is impossible to find and count all of the individuals. They may be hard to find for various reasons. What are the reasons they may be hard to find?

Materials:

• field measuring tape
• vials or cup
• paper
• acrylic paint
• paint applicator
• pencil

Procedure:

1. Each class will be assigned to look at a specific area on campus.
2. One team will be in charge of measuring the area (length x width), describing the habitat, and creating a map.
3. The other teams will be assigned to a plot within the study site. Within that plot, students will look for and mark every spider they can find. Mark the spiders by placing a dot of paint on their back. Keep count of how many spiders you mark. Each team will have their own color of paint for their plot.
4. Meet with the measurement team to have your plot area outlined on the map.
5. Return to the classroom and write the information (how many spiders were marked in your study site) on the board. The measurement team will copy down this information on a separate piece of paper and turn it in with the map.
6. 3-4 days later, we will return to the study site. Teams will work in the same plot as before. Find and count all spiders. Record how many were marked and with what color and how many spiders were unmarked. The measurement team will continue to add detail to the map of the study site. Report your data to the measurement team to be included on the map.

Data:

1. In class, information (# of spiders recaptured, colors and # of marked spiders, and # of unmarked spiders for each plot) is placed on the board. Make a table to show the data.
2. Calculate the number of spiders that live in the study site using the Lincoln Index:

• N = number of spiders that live in the study site
• n1 = number of spiders captured on first day (by entire class)
• n2 = number of spiders captured on second day (by entire class)
• m = number of marked spiders that were captured on the second day

 

3. Calculate how many insects are being eaten per week by spiders on the study site using feeding rates determined with our spiders in class. How many insects are eaten in your study area monthly? yearly?

 

Results and Conclusions:

1. Check the locations on the map made by the measurement team. Did any of the marked spiders move to different plots? What are some reasons why spiders may move to new areas? Were any webs occupied by a new spider?
2. Describe the distribution of spiders in the study area. What factors may account for this distribution?
3. Are spiders limiting the numbers of insects in the study area? Do you think spiders are a benefit to farmers, gardeners, and humans? Why or why not?
4. Further discuss your results on the impact of spiders on insect populations. Explain how your class data support your conclusions.
5. What assumptions are being made in a Mark and Recapture study?

 

Abstract:
Write a one paragraph (5-7 sentence) abstract summarizing this experiment and the information gathered by doing this experiment.

 

The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers
warder@email.arizona.edu