Any ideas why the buttercream would make holes like this? do i just need to add more and smooth it out better?

i feel like when it sits, the holes appear..that werent there when i put it on..but maybe thats just in my mind!

Yes, I would just go over it again...probably air bubbles or air pockets (same thing, I guess) popping and leaving holes.

Thanks...and air bubbles are caused because of ?

Is it something to do w/ how long the buttercream gets mixed in the mixer?

If you have more of the b/c, Just smooth it good in the bowl with a spatual. Just mash and turn it over. etc. till you see it is nice a smooth. reapply where you need it. let it set and then smooth ever how you finish smoothin. Next time, yes, be sure it looks smooth in your mixing bowl. Don,t beat it wide open. Most of the time, if you b/c cream come up over the blade , then you will get best results. Good Luck. I think you can fix your problem. You can also use hot water spatula, and don,t let it be wet, and smooth around this area also. Some people do spray (my friend does) with warm-hot water and then use the spatual. I have done this also. Lots of ways can get you there.

I always mix my icing with a full bowl over the beaters and I still get air bubbles. It is such a mystery to me.

Try adding a little more water. I always make buttercream on the soft-ish side of the recipe, these holes then smooth right out.