FOCUS: Odd bumps and lumps on twigs, buds, and weed stalks might be galls, swellings on plants that are homes for an insect, mite, or other organism. A gall-maker causes its particular host plant to form a bulge in which it will live and feed for a time. Galls on buds, twigs, roots, or leaves of plants provide a safe home for the gall-makers and are an essential part of their life cycles.
INTRODUCTION
Objective: To begin to explore and ask questions about galls.
Ahead of time, collect a selection of goldenrod stems with goldenrod ball galls on them. Make sure to cut the stems so they are long enough to show the gall(s) and the seed head at the top of the stalk. Pass out a goldenrod ball gall and magnifying lens to each child, and ask children to observe and describe their gall.
Materials: ball gall on a goldenrod stem of either tall goldenrod (Solidago altissima) or late goldenrod (Solidago gigantea), one for each child; magnifying lenses.
THAT’S MY GALL
Objective: To make observations and ask questions about goldenrod ball galls.
Using the goldenrod stalks from the Introduction, encourage children to look closely at their galls. You may wish to prompt their investigation with these questions:
- Is it part of the stem or something attached to it?
- Are there any holes where something went in or came out?
- Any bumps on it? Do they look like any other bumps on the plant’s stem?
- Is the gall smooth or rough? What about the stem? If it’s rough, what makes it feel that way? (hint: use magnifying lenses to look closely)
- When was it formed? While the plant was growing or afterwards?
- Did the plant continue to grow after the gall formed?
- Did the plant make flowers or seeds?
- What could this part be for?
What are some other questions they have about the galls?
Divide the class into two groups. Now collect the galls from each group separately, spreading them out on a tarpaulin. Have children come up in pairs or small groups to find their own goldenrod stem. For older children, add a couple of extra galls to make it harder. Are the galls identical? What are some differences? (Size, location on stem, roundness, coloration, etc.)
Materials: for each child: goldenrod ball gall from Introduction, magnifying lens; a few extra goldenrod ball galls, tarpaulin.
FLY-AWAY GALLFLY
Objective: To model the life cycle of the goldenrod gallfly.
What would it be like to be a gallfly? Explain to the children that they will pretend to be a gallfly as you read a story about its life cycle. Have children spread out and kneel on the ground. Each time they hear you say the word, “eat,” have them make chewing noises, or you may give each child a small celery or carrot stick to nibble. Read the narration as the children act out the story.
Fly Away Gallfly Narration
(Optional: hand out a celery or carrot stick to each child, but have them wait for directions before eating it.)
I’m going to tell you a story in which you get to imagine what it would be like to be another creature. While you listen to your life story, make chewing noises or take small nibbles from your snack when you hear the word “eat”.
You are all tiny gallfly eggs, and I am your mother. I have set each of you inside the bud of a young goldenrod plant. Curl up and on the count of three, you will hatch as a tiny larva. One, two, three!
You’re a hungry little larva inside a soft green goldenrod shoot. You eat your way down into the stem. As you eat, the stem swells around you, making a sturdy home. Warm days and nights go by. It’s dark inside your gall, and you are all by yourself, but you don’t mind—you just want to eat! You eat the juicy, rich goldenrod as your gall sways gently in the summer breezes. Here you are safe from dangers.
Summer turns to fall. You have been eating so much that you are now quite a round, plump little larva. The walls of your gall are getting harder and not as tender and juicy.
Something tells you to get ready for the time when you will leave your gall. You need a tunnel, so you eat one. You eat your way right up to the thin, green wall, almost out into the bright sunlight—but you don’t want to leave yet! It’s cold out there, and you are still just a larva. No, you turn around and go back to the center of your gall. One last nibble and all your eating is done. It’s time to rest. Winter in your gall home is long. But you are half asleep, and you don’t mind the cold or dark.
Eventually, it starts to get warmer. It’s spring! In the warm weather, strange things happen to you. You become a pupa, quietly changing, and when you wake from it, you feel different. You stretch and move, and you crawl out to the end of your tunnel. You place your head against the wall the wall, and push—stretch and push harder—and the wall breaks. Suddenly you are out in the sun (stand up and stretch). The sun’s rays warm and dry your new wings for you are now an adult! You have changed into a special little fly with brown wings and a golden-brown body. You will soon fly away in search of a mate, and perhaps one day you, too, will place a tiny egg carefully inside the bud of a young goldenrod plant. Fly away, gallfly!
Afterwards, ask the children how long it takes for one complete life cycle. (One year.) Review the life cycle using the Gall Life Cycle cards. The gallfly adult lives for about two weeks; how much time does the gallfly spend inside the gall? (About fifty weeks – nearly a whole year.)
Materials: Fly-Away Gallfly narration, Goldenrod Ball Gall Life Cycle cards; optional: celery or carrot sticks.
PUPPET SHOW “A Swell Day”
Objective: To meet a variety of different kinds of galls and learn about their gall-makers.
Perform the puppet show, or have a group of children perform it for the class. Afterward, ask questions to review the key details and vocabulary in the story. Hold up each gall puppet and ask where the gall forms on the plant (stem, leaf, bud, etc.) and what kind of gall-making insect is housed by the gall (gnat, wasp, fly). Note that some are still inside the gall in winter (goldenrod gallflies) and others are empty (oak apple gall, raspberry knot gall) because the insect has already emerged.
Materials: puppets, script, stage.
JOURNAL ACTIVITY
Objective: To record observations about the detailed structure of a gall.
For older children (Grades 3-6), give each small group a set of six to eight different galls to examine in a white dish basin. Have each child pick one or two of the galls to draw. If done on separate pieces of paper, these drawings can be used for Gall Match (below) instead of (or in addition to) the gall photographs. Can they tell which part of the plant (stem, flower, leaf) forms this gall?
With young children, have them make a sketch of a goldenrod ball gall since these are easier to draw. Afterward, have children share their drawings in small groups.
Materials: A variety of galls, at least one per child; white dish basins, journals or clipboards and paper, pencils; optional: colored pencils.
GALL MATCH
Objective: To look for patterns of similarities and differences in a variety of galls.
Set out six to eight different galls (in white dish basins) at three different stations. Place a set of Gall Photo cards (or the children’s gall drawings from Journal Activity) at each station showing the galls in that display, and for older children, an extra card or two. Have the children work in small groups and visit each station to view the variety of galls on display and match them with the Gall Photo cards. Afterward, have them reshuffle the cards and move to another table to match up those galls. Provide copies of What Some Gall-makers Look Like to view pictures of some of the different insects and learn about their life cycles. Have children noticed any galls outdoors? What plants might be good places for finding galls?
Alternatively, hand out a card to each child and have them visit each station and try to find the matching gall, then leave their card in that basin.
Materials: Gall Set: about twenty different kinds of galls, three white dish basins, Gall Photo cards, copies of What Some Gall-makers Look Like.
GALL QUEST
Objective: To look for evidence of galls and gall-makers.
Ahead of time, scout out plants on the school grounds where galls are present and mark with surveyor’s tape. Have the children work in small groups with an adult. Bring along a Gall Guide showing photos of some different galls. Have each group stop at each marked plant and look for the gall or galls on it. Try to find matches on the Gall Guide. Can children find any galls on other plants as well?
If available, have children visit a patch of goldenrod. Have children look for things on the list below:
What You Might Find in a Patch of Goldenrod
- The biggest ball gall; the smallest ball gall
- A gall with chickadee damage
- A gall with a woodpecker hole
- A double gall (two on one stem)
- A triple gall (three on one stem), or more than three
- Two galls joined together into one
- A goldenrod bunch gall
- A goldenrod elliptical gall
- A gall with an exit hole
Have children mark a few goldenrod stems with surveyor’s tape to check later in the spring for exit holes or evidence of predation by birds.
Materials: surveyor’s tape and marker pen, copy of Gall Guide for each small group.
INSIDE A GALL
Objective: To make observations of gall contents and look for evidence about what might have occurred.
Working in small groups with an adult, select a few galls to open in order to view the contents. Show children the handout, What You Could Find in a Goldenrod Ball Gall, and discuss the different possibilities and how to tell them apart. On a cutting board, the adult should use a sharp, strong knife and carefully cut vertically into the gall about a third of the way through, until you can twist the knife and split it open. (Alternatively, cut galls open ahead of time and tape shut.) Look for a larva, pupa, frass (insect droppings), and for the exit tunnel. Hold up the tunnel to a light to see its transparent covering.
Children often express a legitimate concern about the fates of gallfly larvae and other larvae we disturb. Looking inside a few galls gives us a better appreciation of them and allows scientists to learn more about them. Goldenrod ball galls are very common, so our investigations won’t hurt the population, but it is still important to limit the number that we open. Afterward, collect the gallfly larvae and put them on a bird feeder, in a fish tank, or carefully place them back in their galls, tape the galls shut (don’t cover the exit tunnel!), and return them to their field, where some may successfully complete their life cycles. You could also save a few in jars to observe the flies when they emerge.
Optional: Afterward, show a video of the gall forming on a goldenrod stem, The Goldenrod and the Gallfly, from the Abrahamson Lab at Bucknell University:
http://www.facstaff.bucknell.edu/abrahmsn/solidago/gallfly_video.html
Materials: What You Could Find in a Goldenrod Ball Gall, sharp knife for adult to use, cutting board, a few goldenrod ball galls (no more than one for every three children), clear jars with lids for collecting the larvae and/or masking tape to seal galls shut again; optional: gall DVD, computer and video projector.
UPPER GRADES CHALLENGE: Keying Out the Contents (Grades 5-6)
Objective: To use a dichotomous key to identify the contents of a goldenrod ball gall.
Working in small groups with an adult, select a few galls to open in order to view the contents. On a cutting board, the adult should use a sharp, strong knife and carefully cut vertically into the gall about a third of the way through, until you can twist the knife and split it open. (Alternatively, cut galls open ahead of time and tape shut.) Now have the students follow the Key to Gall Contents to identify insects commonly found inside goldenrod galls. Use What You Could Find in a Goldenrod Ball Gall to see illustrations of the different possible contents, or view these on the online key.* What evidence did they find about the fate of the galls they looked into? How many were empty, how many contained gallfly larvae, and how many contained evidence of a parasite? Afterward, collect any larvae and put them on a bird feeder, in a fish tank, or carefully place them back in their galls, tape the galls shut (don’t cover the exit tunnel!), and return them to their field, where some may successfully complete their life cycles. You could also save a few in jars to observe the flies when they emerge.
*Optional: Use the online Key to Gall Contents at http://www.facstaff.bucknell.edu/abrahmsn/solidago/gallkeyintro.html.
Optional: Afterward, show a video of the gall forming on a goldenrod stem, The Goldenrod and the Gallfly, from the Abrahamson Lab at Bucknell University:
http://www.facstaff.bucknell.edu/abrahmsn/solidago/gallfly_video.html
Materials: goldenrod ball galls, one per two students; Key to Gall Contents and What You Could Find in a Goldenrod Ball Gall for each pair of students, sharp knife for adult to use, cutting board, clear jar with lid for collecting the larvae and/or masking tape to seal galls shut again, metric rulers, magnifying lenses; optional: computer and internet (for using online key), video projector.
CLOSING THOUGHTS
Objective: To share thoughts about galls.
Pass around a goldenrod ball gall and have each child complete this sentence in turn: “My favorite discovery about galls today was __________.”
A STEP BEYOND
Gall Visits: In winter, mark galls with surveyor’s tape; revisit in May to look for exit holes.
Gall Journal: Keep some galls in jars; observe daily to see if any insects emerge. Keep records of changes and any flies or other insects that emerge.
Gall Graphing: Use string to measure the circumference of some ball galls. Graph results for the whole class. What is the range in size? The biggest, the smallest? What is the median size?
Nearby Nature 