What Kind Of Bug?

[lxskllr]

I have a white pine branch that's been detached from the tree for a few years. I used it last year to stack firewood on. I was rearranging my wood this year, and saw these interesting cavities in the branch. Didn't find any critters, but I think I found the remains of some web like material in a couple holes digging in with my knife. Any idea what was in there?

[LarchMan]

It's tough to say from the picture but given the size of the chamber and the description I'd wager that it was some type of Monochamus or other large sawyer beetle.  Those would be the pupal chambers that you are seeing.  I'm guessing you'd see feeding activity deeper in the wood as well. 

That's based on an educated guess from someone on the west coast for what that's worth.