You may recognize the bur oak in this page from previous photos. It is a magnificent, ancient bur oak in Kirklevington Park. I visit it often. Last week I was looking at the tree in the late afternoon and noticed a few leaf fragments on the ground. The next morning, I came back and saw that the tree had been totally defoliated overnight, stripped of nearly every leaf. After a few days, it began to refoliate - to produce a new crown of leaves. Spring defoliation is very common, but is not very harmful to hardwood trees.
None of the nearby bur oaks were defoliated. Two Shumard oaks had lost a little bit of foliage. It was like a special forces strike on a single tree. Remarkably, the defoliating insects were completely gone by morning, not a sign of them. I don't know what they were.
We'll add more pictures as recovery continues.