Interesting. I went and checked mine and couldn't find any holes like that. A while back I was getting nearly perfect circular holes in my oranges and it turned out to be a woodpecker!

I found a second one. I split it open and there is a very small caterpillar living inside. I have no idea as to what mama looked like.

It's a kind of moth. They've ruined my crops beginning a few years ago. I may have to start bagging the clusters

I just went out and found several caterpillars, small and brown. It seems that they start in the flowers and chew into the fruit as they get larger. It's too late to bag so I'm spraying with Bt right now to put a stop to that.