Quillback nailed it. That Rock Crawler is a fish-catching dude. I don't know the specifics behind WHY they eat it, but they do. Yes, the Wiggle Wart is a fish catcher, too.
I do know that Mike McClelland spent a lot of time getting the Rock Crawler prototypes the way he wanted them. They were released later than scheduled because he wasn't happy with the rattles. I'm glad he and Spro took the extra time because they sure got them right.
Only problem is the bills do tend to break off, so be careful about smashing them against rocks on your cast and don't slap them on the water to clear them of moss, leaves, etc.
If I had one color, it would be phantom brown. Second choice would be phantom green, and then spring craw.