Question
I have an oak tree in my back yard. Part of my back yard is covered with very small brown balls that jump like "mexican jumping beans".
A  friend called tham "oak tree galls". My question is ;can they cause damage to grass,plants, or humans?

Answer
No they will not cause any problems to other plants grass or humans. They will hatch out and enter the soil and emerge as wasps and fly back to the oak leaves and lay their eggs starting the life cycle over. Here is a web link to more information on these insects. http://waynesword.palomar.edu/pldec97.htm