YIKES!!
ME BIG DUMMY!!
I posted this fly, (Knudson Spider) and mentioned it's "Simple tie, because of only two materials, possibly 3, if you use lead wire under the chenille".

WRONG!!
This pattern calls for FOUR materials, because behind the Mallard flank collar, there should be a quite short, 2-3 turns of GRIZZLY HACKLE, to help in keeping the Mallard flared out, when the fly is submerged.

Sorry; me bad, me stupid, me dumb.
Paul