These flies are deadly Trout & Grayling that have a horizontal hackle tied around a post (usually a great sight indicator). Normally fished as a single dry fly on a tapered leader. It is normal to put floatant for example Gink (not on CDC flies) on the main hackle and dry the fly with desicant like Semperfli's Desert Dust when the fly becomes waterlogged and does not sit right on the water.
Allow the para fly to float naturally downstream, if the fly line or tapered leader gets ahead of the fly and starts to drag the fly it will no longer look natural. Perform an upstream mend, flicking the flyline and leader behind the fly so that it continues to the end of its drift without drag.