Galls

Look for galls on leaves and stems. If you see one, you know an insect has been there.

What are galls? Galls are a plant's response to an injury or a foreign object, such as a small animal. Some people think that galls are plant scar tissue that forms around the injury. Gall formation is not entirely understood, but it is more than just scar tissue. The insect or mite in the gall apparently causes the plant to form a gall.

An insect or might lays eggs on or in plant tissues. The plant responds by forming a gall at that site.

Photo of goldenrod gall (in summer)
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Photo of goldenrod gall (in fall)

One very common gall in North America is the goldenrod gall. This gall is formed when a female goldenrod gall fly lays an egg in the stem of the plant.

Photo of fly larva inside gall

The egg develops in the stem through its larval stage and emerges as an adult by biting a hole in the gall to escape.

 
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BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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