I see! It might seem like I've lost the plot but it really is a something I've heard said often. It must be an "irish-ism!" given that I'm from Northern Ireland!
Never heard of this expression, but it's very apt in describing a tangled mess. If you think of an entwined mass of growing peas, then, once they've died off, grapping a handful, (wisp), it's utterly descriptive.