EDIT: I composed and submitted this post before reading xcathodex's post, so that's why it doesn't explicitly recognize xcathodex's suggestion that it's the false butterfly. I'm leaving my post the same, but xcathodex beat me to it and deserves the credit.
Contrary to what Dave Merchant says in Life on a Line, 2nd Edition, I don't think there's any controversy (not these days, anyway) about the identity of the knot called "alpine butterfly."
Well, here's my original post:I avoid the simple term "butterfly" because it is ambiguous. In cases where an author (or caver) discusses the "alpine butterfly" and "butterfly" as separate knots used for rigging applications in vertical caving, my guess is that by "butterfly" they mean what Marbach and Tourte call the
false butterfly.
While it is rarely tied this way, the false butterfly is perhaps best explained as a slipknot partially secured from slipping by a half-hitch tied over it on the slippy side. knudeNoggin may have a more proper functional definition. It looks a lot like an alpine butterfly, but it isn't a secure knot. It's an idea midline shock-absorbing knot, because it slips when shockloaded or loaded heavily (and slips a little in any loading). I am unfamiliar with any valid applications involving loading the loop.
The easiest way to tie the false butterfly correctly (and, to the best of my knowledge, the only method that is commonly used to tie it) is to make like you're tying the alpine butterfly
this way, but to twist the loop back in the opposite direction in step 2. You will have to hold it in this position until the next step, because the overall twist is now zero.
Note that the false butterfly bend should never be used--it may slip all the way through...and if you wanted something to automatically disconnect in a shockload, it's not precise enough to necessarily fail when you want it to either. The existence of the false butterfly bend is probably the most compelling argument against the use of the alpine butterfly bend--it's hard to know for sure that you're looking at an alpine butterfly bend and not a false butterfly bend, and recognizability is an essential consideration in knot choice.
This may not be too helpful, but... you could probably (eventually) get in touch with Al Warild by contacting the operators of the Cavediggers website (which currently hosts his book
Vertical). Their email is on the bottom of
their home page.