What snacked on Lucas?

Yesterday as we were leaving the beach I noticed what I thought was just a small bug bite in the crease of Lucas arm. This morning I noticed they were all over his arm and they were getting HUGE! I don't know what kind of bite it could be. It had to have happened in the car on the way to the beach or at the beach because I put sunscreen on him before we left the house and it wasn't there (or at least visible) when I put it on him. Also he wore his shirt all day at the beach and it covered that part of his arm. I am thinking something got stuck in his shirt and had to bite it's way out. Anyone have any ideas?

The original bite I noticed yesterday was in the crease of his arm. It has gotten HUGE.

The outside of his arm by his elbow.

Close up

The thing on his elbow is bigger than a quarter.