Spotted this small object on a swamp white oak leaf yesterday.
With help from iNaturalist and Tracks and Signs of Insects, I learned that it’s an egg of a Polyphemus Moth (Antheraea polyphemus).
You may recall that I found a half dozen of the large cocoons of this species over the winter. I’ve seen several reports of adult moths being spotted around Brooklyn on iNaturalist, although I haven’t seen any myself. But they’re obviously finding each other…
Good to know another generation has a chance.
Backyard and Beyond 
Interesting that it is on the top side of the leaf.
Isn’t it? Just jumps right out at you.
Nice catch. Something that small could easily be missed.