hahah I love these questions!!! :) He has ants in his pants = he can't sit still, he is too agitated about something. Imagine if your pants/underwear were full of ants biting you, you would keep fidgeting (moving) about! It would be very difficult to stay still. In the same way, if you are excited or nervous about something, you tend to move about a lot! :)

It means you are fidgety moving about a lot someone who does not sit still

Well... When you're getting nervous about something, or enthusiastic, worry... Example: C'mom, you must calm down! you've got ants in your pants

might be thrilled or worried

Means someone wriggles, an idiom about the way someone walks. In your example the usage is a little different though. Seems to mean hassling, hurrying etc.