[VFB] Fluttering caddis question

[J&A Burbank]

I have a question and maybe it's stupid but never the less I'm going to ask. As I look at all the different patterns for a fluttering caddis I notice they all have a wing on them, usually elk or deer hair, behind the hackle. My question is this, if it's a "fluttering" caddis why does it have it's wings laying on it's back? Shouldn't it just have heavy hackle to give the appearance of a fluttering wing? Can someone please explain this to me?   Thanks   Jim