Golden Rod Gall Size

A CIBT Lab Exercise in Ecology and Evolution

The article, Just lookin' for a home. Natural History, Sept, 1998 by Arthur E. Weis, Warren G. Abrahamson, is useful supplemental reading for this lab. Natural History magazine is not currently carrying the lab on it's web site but copies can be found at various library sites where you may or may not be able to get full text access due to copyright restrictions.



This investigation examines natural selection and coevolution using goldenrod (Solidago canadensis), its stem gall insect (Eurosta solidaginis), and associated parasites, parasitoids, and predators that feed upon the stem gall insect (i.e., Eurytoma obtusiventris, Eurytoma gigantea, Mordellistena unicolor, and birds). Through measurements of gall size and an investigation of events occurring within the galls, a correlation between gall size, frequency of predation, and type of predator can be made. An analysis of histograms and data tables charted from gall measurements and frequencies of various events leads to the conclusion that parasitic organisms select goldenrod galls within specific ranges of size. A statistical analysis using standard deviation and tests of reliability also lead to the conclusion that the forces of natural selection and coevolution are operating within this stem system.


Appropriate Levels

Concepts taught in this investigation are appropriate for all high school biology students. The main write-up is for Regents Biology. There is an extension for AP or Honors level students. There is also a version directed at general or school group students.


Time Required

Three to five lab periods are required to describe the complex ecology under study, to learn to use the Vernier calipers, to measure the galls, and analyze the gall contents.



Special equipment needed:

  • Stereoscopic microscopes or hand lenses
  • Vernier calipers for the whole class


Resources available for this lab:

Read a student lab report of this activity. This report was provided by George Wolfe, Director, Dominion High School Academy of Science, Sterling, Va. View it here.

View a slideshow of the gall and its denizens. Twenty four slides depict the common organisms found in this goldenrod-gall fly system. View it here.

Copyright for this material is held by Cornell University, the Cornell Institute for Biology Teachers (CIBT), the Center for Nanoscale Systems Institute for Physics Teachers (CIPT), and or West Hill Biological Resources, Inc., 2014. This work may be copied by the original recipient from this web site to provide copies for users working under the direct supervision of the original recipient. All other redistribution of this content without the express written permission of the copyright holder(s) is prohibited.

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Mary Colvard, Cobleskill High School, Cobleskill, NY

Tom Vawter, Wells College, Aurora, NY