My name is Ann Chanon, and I am the Agriculture and Natural Resources Extension Educator for Lorain County. What you are observing falling from your oak tree has been called a fuzzy gall, woolly gall, or plush gall. These galls occur on members of the red oak group including, pin oak and northern red oak. Fuzzy leaf galls look like dense wads of wool attached to the veins of the leaf. They are often yellow or orange in color during the summer, fading to brown in the fall. A tiny adult insect inserts an egg into the vein of a leaf. The gall is the plant's response. The insect larvae grow and develop inside the gall during the summer. In the fall, the galls can detach from the leaf with the mature larvae inside. The insect will then complete its next stage of development while overwintering and emerge as an adult next spring. This insect poses no harm to humans, pets, or other plants. It is specific to oaks. Although the galls can have an ugly appearance, they do not affect the health of well-established trees. The insects are present every year, but most of the time, their numbers are low enough that the galls go unnoticed. Periodically environmental conditions allow large numbers of them to survive and reproduce. So even though you have leaf galls this year, they may not appear again next year. There are no insecticides that are effective because the adult insects are tiny and not easily observed, so the timing of an insecticide application would be difficult, and during the larval stage, they are well-protected from pesticides within the galls. Raking and removing both the galls and any fallen leaves with the galls still on them can reduce the number of overwintering larvae and might help prevent the problem next year.