Wildlands Capture/Recapture Experiment

Grade Levels: 4-12 (Note: This experiment can be simplified or made more challenging depending on the developmental levels of your students. See Teacher Information.)

Description: By using an already tested scientific research method, students can determine the numbers of a mobile population of insects. Grasshoppers are captured, marked, and then recaptured. Students learn how to use an algebraic formula to determine their populations.

Approximate Time Involved: One 30-minute classroom planning session; (first day outside) 10 minutes to conduct sweep; 20 minutes to count, mark and release animals; (second day outside) 10 minutes to conduct sweep, 10 minutes to count and release animals); 10 minutes to enter data online, one or two 30-minute classroom sessions to examine results, state conclusions, draw inferences, and make recommendations.

National Science Standards Addressed:

Content Standard A: As a result of activities in grades K-12, all students should develop

  • Abilities necessary to do scientific inquiry
  • Understanding about scientific inquiry

Content Standard C: As a result of activities, all students should develop understanding of:

  • (K-4) Organisms and environments
  • (5-8) Structure and function in living things
  • (5-8) Populations and ecosystems
  • (9-12) Interdependence of organisms

Program Standard D: The K-12 science program must give students access to appropriate and sufficient resources, including quality teachers, time, materials, and equipment, adequate and safe space, and the community.

  • Good science programs require access to the world beyond the classroom.

Teacher Information:

The Wildlands, schoolyards, fields, parks and other open desert areas provide students with a great opportunity to examine and test the capture/recapture method used by scientists to determine the population size of a mobile animal such as the grasshopper. The capture/recapture process is just one way to determine animal population sizes and it, like the others, is not 100% perfect. NOTE: Encourage your students to search the Internet and other sources for more information about ways in which scientists determine animal populations.

A number of grasshoppers* will be captured, marked and released during the first day of the experiment. The next day a second sample of grasshoppers will be captured from the same area. The following assumptions must be met in order for this sampling technique to be valid and useable:

  • All of the grasshoppers in the population of a given area have an equal chance of being caught.
  • There is no change in the ratio of marked to unmarked grasshoppers. To make certain this holds true, there must be no significant additions or subtractions to the marked population of grasshoppers that is different from that found in the overall population of grasshoppers.
  • Marked grasshoppers distribute themselves equally throughout the population so that both marked and unmarked grasshoppers have the same opportunity to be captured in the second go-around.

*It was thought that grasshoppers would be the most prevalent organism, but you may choose to capture/recapture another organism that is more common to your schoolyard (crickets, leafhoppers, moths, etc.)

If the above assumptions are met, the number of grasshoppers caught in the second sampling will be proportionate to the number of grasshoppers in the entire population. The total population of grasshoppers for a given area can then be estimated using the following formula:

  • If N/M = n/R, then N = (M)(n)/R
  • Where N is the total population size to be estimated
  • M is the sample of grasshoppers that was captured, marked, and released
  • n is the number of grasshoppers captured the second day
  • and R is the number of marked grasshoppers that were recaptured on the second day.

What the capture/recapture equation is saying is that the ratio of the total population of grasshoppers to the total number marked on the first day is equal to the ratio of the total number caught on the second day to the number of marked grasshoppers that were recaptured.

  • (Example: M = 32 grasshoppers caught, marked & released on the first day, n = 40 grasshoppers caught on the second day, R = 20 recaptured, marked grasshoppers. Therefore N/32 = 40/20 and N = (32)(40)/20 or 64)

Challenging Your Students to Be Problem Solvers:

To make this experiment more challenging to your students, you might just want to pose a question or problem such as: Based on the research information you have collected on capture/recapture techniques, design and conduct an investigation to determine the size of a population of mobile animals living in the schoolyard. OR Using the information provided above, design and conduct an investigation to determine the population size of the grasshoppers living in the schoolyard. OR Conduct the grasshopper capture/recapture experiment in two or more different habitats (schoolyard, park, open desert areas) and compare your results. What factors may have influenced the difference in grasshopper population size found in each habitat?

This should become a team exercise where your student groups might each conduct Internet research on capture/recapture techniques, design or choose the investigation and habitat, develop and write a question or hypothesis, list the materials they will use, the number of each item, and a procedure. NOTE: An excellent way to assess this activity is to have the teams repeat each other's experiment to see if they achieve the same results. This will also replicate the real world challenges facing a research scientist.

Needed Materials: Sweep nets, collection jars or half-gallon Ziploc plastic bags, pencil and clipboard, small paint brushes and several colors of model paint (magic markers seem to work as well and may simplify the marking process) (NOTE: The number of each item needed will be determined by the number of student groups you plan to have perform the investigation.) (NOTE: You can purchase inexpensive 5-gallon paint straining bags for around a $1.00 each at your local Sherwin Williams paint store, or other paint stores. They can then be sewn onto coat hangers to make inexpensive sweep nets.)

Safety Rule: When using a sweep net it is likely that some stinging insects and spiders may be captured in the process. Remind your students to use caution when removing organisms from the sweep net. Special care must be taken not to injure the organisms that are to be marked and released.


Student Information: The following information will provide you with the steps for conducting your capture/recapture investigation and marking the organisms you have caught. It is important to hold all of the variables constant except for those that are being manipulated. Constant (or controlled variables) would be such things as: the size of the capture/recapture area, the size and shape of the sweep net, the time of day the experiment is conducted, the way in which the sweep is performed, etc. Manipulated (or independent) variables would be those things that we change to see if the response will be different. In this case it might be different habitats, weather conditions, times of the day, etc. NOTE: To guarantee accurate results, you can only have one manipulated (independent) variable during an investigation.) The responding (or dependent) variable for this experiment might be the number of animals you catch in each of your habitats. If you are only conducting this investigation in your schoolyard, then you will want to compare your capture/recapture data with other online classes to see if there are similarities or differences in your habitats and your results.

The reporting form for this experiment is set up so that you can identify the habitats you want test, identify the animal population(s) you plan to count, and provide additional information about your experiment. NOTE: Remember that a good scientific experiment is repeated a minimum of three times. To accomplish this, several student groups can each conduct the investigation in several identical habitats around the schoolyard and then compare their data to check for accuracy. If their data is similar, they may want to compile an average and submit it as a group. If there are major differences, a discussion should follow to determine what may have caused these differences in the results.

Steps to Conducting a Capture/Recapture Investigation

1. If possible, choose a location approximately 50 meters long and wide enough so that all of the groups' sweepers can stand at an arm's length away from each other. Provide each group with a different color paint or magic marker.
2. The individuals with the sweep net (sweepers) will walk the length of the study area, sweeping the net back and forth in a consistent figure-eight manner so that the opening of the net is first to sweep the area.
3. Stop every five meters and place your captured organisms (grasshoppers) in your collection jar or Ziploc half-gallon bag.
4. Other members of the group can take the jar or bag and carefully begin marking the grasshoppers by placing a small spot of paint or magic marker mark on the top thorax of the grasshopper just behind the head region. NOTE: Do not get any paint or marker on the grasshopper's eyes.
5. Use the pencil and clipboard, or calculator with memory, to record the number of grasshoppers you are marking as you go.
6. Carefully release the grasshoppers back into the same approximate area as soon as the paint or marker dries.
7. Complete the sweep of the entire area length, capturing, counting, marking, and releasing the grasshoppers as you go.
8. Return all equipment to the classroom and complete an inventory to make sure nothing was left in the study area.
9. On day two, repeat the procedure described in steps 1-3 at the same location.
10. This time, keep track of the total number of both marked and unmarked grasshoppers as you go. Once you have taken a count, carefully release the grasshoppers back into the same area.
11. Each collaborative group should now have the data you need to plug into the formula described above. Once your group has completed the formula, compare your results with other collaborative groups.
12. Add all of the collected data for the entire class and plug that into the formula.
13. Create a data table to display, compare and analyze your results.

Below is a list of questions that can be used to stimulate student discussions. If your students are at a developmental level where you are able to challenge their higher level thinking skills, then only present them with the first set of questions from each group below. Use the second list of questions as a way to stimulate thinking when you students seem unable to expand their knowledge on their own.

Examining Results

Discussion Questions that Require More Critical Thinking Skills

  • What were your results and conclusions for this experiment?
  • What could you infer based on your conclusions?
  • How would you design and/or conduct this experiment differently the next time?

Discussion Questions that Require Less Critical Thinking Skills

  • Did your results match those of the other collaborative teams?
  • If your results were different, what do you think might have been the reason?
  • Did all of the collaborative groups end up with the same results? Why do you think this was the case?
  • Were the results somewhat similar to each other? Why do you think this was the case?
  • If you were able to compare your data to that taken at a different location in the schoolyard, were the results somewhat similar? Why do you think this was the case?
  • Did the outside temperature have any impact on the number of animals caught?
  • If you were able to conduct this investigation in other habitats, what comparisons and differences were you able to note?
  • What factors might impact the number of animals captured and recaptured? How could you test your assumptions experimentally?

Examining Local and Online Results

Discussion Questions That Will Require Critical Thinking Skills to Compare Individual Data to the Data Collected by Others

  • How did your results compare with the results of others?
  • What conclusions can you make when you compare your results with the results of others?
  • What inferences can you draw from your additional conclusions?
  • How would you design and/or conduct this experiment differently based on the information you now have?

Critter Links

Entomological Society of America This site has a special "kids" page for insects.

Monarch Watch Participate in a migratory census of butterflies.

Iowa State Department of Entomology This is a good source for information on insects, including some insect recipes.

Children's Butterfly Site This butterfly site is maintained by the United States Geological Survey.

The Butterfly Website Learn more about the fascinating world of butterflies.

Butterflies, Moths, and Cool Bugs Browse this collection of insects from Havana Junior High's annual Adopt-An-Insect Project.

Young Entomologists' Society, Inc. If you really like to explore the insect, spider, and minibeast world, check out this site and become an amateur entomologist.

This activity was adapted from a lesson plan developed for

with the contribution of Jill Schimmelpfennig and Mike Schneider.  An on-line version can be found @ http://web.stclair.k12.il.us/splashd/hrockexp.htm