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Shooting the Poop

More than Good Housekeeping?

Co Authors:

Kylee Grenis

Tri-County Health Department

Laurel C. Cepero
Department of Biological Sciences
University of Denver

Mayra C. Vidal
Department of Biological Sciences
University of Denver


This group-based case study is based on research by Dr. Martha Weiss using silver-spotted skipper caterpillars (Epargyreus clarus (Lepidoptera)). These insects perform the unusual behavior of flinging their frass (excrement) great distances away from their leaf shelters. This charismatic study system, besides being appealing to students, has the advantage of having several plausible alternative adaptive hypotheses to investigate. After viewing a brief PowerPoint presentation that introduces the perils of caterpillar life and a video demonstrating their unusual behavior, students brainstorm hypotheses and experiments to test them. Students then receive a set of datasheets and questions that guide them to an understanding of the actual experiments that Weiss conducted. The conclusion of the case provides an opportunity to discuss the difference between statistical and biological significance, a distinction often neglected. This case was developed for introductory-biology major undergraduate students, but can also be used in any undergraduate course involving the evolutionary concepts of adaptation and fitness.

  • Review adaptation, fitness, and selective pressures.
  • Review the role of adaptation in evolutionary processes.
  • Know how to measure fitness and/or fitness proxies.
  • Formulate hypotheses about adaptive traits.
  • Design experiments to evaluate hypotheses.
  • Interpret figures and analyze statistical reports to evaluate the validity of proposed hypotheses.
  • Determine whether statistical significance equates to biological significance.
Keywords: Adaptative hypotheses; biological significance; experimental design; fitness measures; anal comb; defecation; Epargyreus clarus; frass; faecal pellets; Hesperiidae; leaf-roller; Polistes; shelter-builder; Weiss
Topical Area: N/A
Educational Level: Undergraduate lower division, Undergraduate upper division
Formats: PDF, PowerPoint
Type/Method: Directed, Discussion
Language: English
Subject Headings: Ecology   Evolutionary Biology  
Date Posted: 3/8/2016
Date Modified:
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Supplemental Materials

The PowerPoint presentation below introduces caterpillar life, shelter building activity, and frass flinging behavior.


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