Nowhere in nature is the dependence of animals on plants more evident than when studying plant galls. A gall, an abnormal growth of plant tissue, is produced in response to substances injected by a mother insect when she lays her eggs. The purpose of the gall is to provide a home for the immature insect. It provides both food and shelter, keeping its occupant safe from predators.

Each gall-forming insect produces a specific kind of gall, usually on just one species of plants. The goldenrod stem gall, caused by a small fly, is an easily recognized rounded swelling found on stems of the Canada goldenrod.

The female fly lays her eggs on the stem in spring. In June the eggs hatch and each larva that bores successfully into the stem causes a gall to form around it. Protected all winter and surrounded by a constant food supply, the larva pupates in spring, finally emerging from the gall in late spring as an adult.

The following activity, designed for children ages 6-10, focuses on goldenrod galls, easy to find in late fall.

Materials:

Goldenrod galls (one per child, collected on hunt)

Crackers (one per child)

Preparation:

Scout open fields and forest clearings in the local area for tall goldenrod plants just past the flowering stage with round swellings on the upper stem. Make sure there are enough gall-bearing plants for each child to find one.

You will need to be able to describe the small grub-like larva that spends the winter within the goldenrod gall. Do your homework! Photographs of goldenrod galls and all stages in the fly’s life cycle can be found at several Web sites, including http://www.fcps.edu/StratfordLandingES/Ecology/mpages/goldenrodgallfly.htm.

The activity:

Take the children on a gall hunt! Have each child collect one gall by breaking off the stem a few inches below the gall.

Back home, gather the children together and briefly explain the fly’s lifecycle, describing the small larva that inhabits the gall. If possible, show them the Web site photos. Ask the children to examine their galls, looking for tiny exit holes. Explain that each hole, made by the larva in the fall, will serve as the adult’s spring exit route.

Read the following story, asking the children to imagine that they are the characters. Give each child a cracker, telling them to eat it only when directed to.

“You are about to become tiny, defenseless creatures. Very quietly, get your jackets and find a place where you can be protected, but where you can hear my voice. Crouch, become as small as you can, put your jacket over your head and be very silent. Close your eyes.

“It is fall now, the days are growing shorter and nights are cold. But you can’t see the daylight nor feel the chill; you are snug in your gall home. You can eat, your food is all around you. Eat, rest, and eat again. (The children should eat their crackers now.)

“The leaves have fallen, beaten to the ground by gusty winds and pelting rain. Soon autumn turns to winter. Snow comes. The pond turns to ice. You are safe in your gall home. But you are alone and it is dark.

“The sun is higher now, owls are nesting, streams are thawing, and you are growing bigger. Warmth, snow melting, sap running. You sleep your final sleep, deep inside your private gall. The time has come for you to change.

“The days grow longer and warmer. Grass is green and flowers bloom. Your gall home is warm and dry. You feel the urge to stretch and move, stretch and move, and suddenly you are out of your gall, standing tall, soaking in the sunlight, drying your wings. You are an adult.”