Possibly sawfly larvae, maybe scarlet oak sawfly? They travel in gangs.

I just saw another leaf or two that had been damaged. Hope this is all for the season.

Thanks!

That's exactly what they are! I think they're really cool looking, don't you? There are not too many things that allow you to look into their 'innards'.

For the most part, these sawfly larvae do cosmetic injury and the tree will recover from the assault and leaf out normally next season. Treating them is not recommended unless it happens a few years in a row, which can weaken the tree.

Lots of other critters will move in to feast on these pests, another reason to avoid spraying.

Scarlet oak sawfly on northern pin oak, who'd have thought!

I wasn't alarmed, there was only a few small areas on two different small trees, with about 4 leaves total. And so small, even the areas that were skeletonized were small.

First time I noticed this kind before.