To enhance student motivation, do "What's Inside Goldenrod Galls?" prior to this activity.

TOPICS:  Insects, classification, ecology

LEVEL:  Middle or high school

TIME:  45 minutes

ADVANCE PREPARATION:  Collect galls yourself, with the class, or have students collect galls as a homework assignment.  You may wish to collect galls 3-4 weeks in advance and store them in a jar at room temperature to allow adult insects to emerge. (This works from January - April, but not in the autumn.) .

MATERIALS: DO NOT USE RAZOR BLADES for this activity.  They break too easily.  We suggest double-edged hand pruners. These cut into galls allowing student to safely break the gall open without cutting the animal inside, or their fingers. Cheaper alternatives include sturdy pocket knives or one-piece scalpels used with gloves .

SAFETY NOTE: If knives are used. Galls are round and hard, and may cause the knife to slip aside suddenly.  Practice opening the galls yourself, and then demonstrate proper techniques to students.  We strongly recommend the use of hand pruners.

QUESTIONS 4-8 require higher-order thinking skills.  We recommend that you discuss these questions with your class before having students write out their answers.  You may also wish to consider questions 2 and 3 from "What's Inside Goldenrod Galls?" at the same time .

1. Goldenrod plant .

2. Gall fly larvae are herbivores and are usually the most abundant insect in galls. Students will not realize that each wasp or beetle means a gall fly was eaten. Thus their numbers will not reflect true gallmaker occurrence. Students should be made aware of the principle that predator populations are usually smaller than prey populations .

3. Obtuse wasp and giant wasp larvae are predators that consume gall fly larvae.  Giant wasps are usually more abundant than obtuse wasps .

4. Answers will vary; accept all that do not contradict data.  Many webs might fit the limited data available to the class.  (See answer to question 6) .

5. Birds or small mammals are reasonable guesses.  Actual winter predators may be woodpeckers, chickadees, nuthatches, mice, or squirrels .

6. Solid lines are typical class results.  Dotted lines are shown in the event that mordellid beetles are found:

Chance (random variation) can make small population samples appear different from actual population sizes.  (As an example, if you choose one human family at random, the sex ratio of boys to girls may be very different from the l:l ratio of the general population).  Also, each predator (gall wasp or beetle) represents one eaten prey insect (gall fly).  Increasing the fly abundance data to include the gall fly larvae eaten by wasp predators may explain some differences.  For example, if a student counted 4 gall fly larvae and 6 wasps, the original number of gall fly larvae in the population was 10 .

7. Sun .

8. The immediate energy sources for insects are the goldenrod plant or other insects.  The ultimate energy source is the sun.

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A more complete key can be found in the "Goldenrod Food Web Dynamics" activity.

STEP 3b.  The species name gigantea means "giant".  However, the "giant" wasp larvae is actually the smaller of the two common wasp predators.

NOTE:  A small mordellid beetle larva is sometimes found in the wall of a goldenrod gall.  If it bores into gall chamber, it may eat the gall fly or wasp larva along with the goldenrod plant, leaving a pile of gray sawdust in an empty chamber.