Yes it looks like the Squash Vine Borer. I am sorry to say I am quite familiar with this kind of damage. I operated once on the vine (cut it open and take out the worm) but I found it really gross. If you can get the worm/maggot out, you can re-bury with some soil and sometimes it will salvage the plant. On some vines you can bury the roots that develop along the vine. There are lots of ideas about how to prevent them. You can search here for those disussions. For me, I just may give up on growing squash. I usually get a few and then this happens. Last year I planted a zuke on the front deck in a pot just to see if I could escape the SVB and didn't.
Good luck and hope others will chime in.
Karen

Butternut squash vines are not hollow like pumpkin vines, so they don't make a hospitable home for the SVB. It may be that the larva was unable to do much damage. Butternuts like to root along the nodes of the vine, so if you can't find any more signs of the borer, burying it under a few inches of soil should help the vine.

Thank you both very much. It looks to me as if something was trying to get in there, but wasn't completely successful. I could not find a hole. I will look again in the morning and bury it if all seems ok. I am not above some surgery if needed at some point. I used to be squeamish, but killing bugs is part of my daily routine now! Karen - sorry to hear that you have lost zucchini plants to this nasty thing. :(

I know what you mean about "used to be squeemish" but now killing bugs just being part of your routine. I am at war w/ the squash bugs too. Up until today I've been squishing all ages eggs, nymph, and adult. But I read a post that said they used a dust buster (hand held vaccum) for theirs, so I tried today and it was amazing much quicker then squashing the eggs. Doesn't seem to work well w/ the adults still squishing them, but I'm sold on vaccuming my garden.

I like the vacuum idea, Kassaundra! I killed (with my hands) an adult squash vine borer moth tonight. He was not expecting me, apparently! So satisfying!! I will give the vacuum a try for the squash bug eggs. :)

P.S. There is no additional damage to the vine (beyond that seen in the pics from a few days ago), so I am convinced that something was trying to get in and gave up. Glad my favorite squash (butternut) happens to be a more resistant variety.