Oak and Maple Galls

Two interesting and beautiful galls are evident right now that you may want to look for. Not

Eye spot galls on red maple. Photo: S.D. Frank

because they will cause much damage to your trees but because they are a marvelous example of how insects have evolved to manipulate plant chemistry and growth for their own purposes. In general galls are formed when an insect injects powerful plant growth regulating chemicals into developing plant tissue.  This causes the plant to develop unique shapes and structures that typically serve as shelter for the insects and their young.  Right now you can see one of the brightest colored galls the eyespot gall on red maple.  This is caused by a midge. Larvae are fully developed and starting to exit the galls from small holes in the underside.  The galls will start to turn brown now.

Woolly sower gall on white oak. Photo: S.D. Frank

The other interesting gall I found yesterday is the woolly sower gall on white oak.  Cynipid wasps lay eggs in developing buds.  Inside these fuzzy balls are many wasp larvae feeding on plant tissue. Cut one open and see.


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