May Freshwater Fly of the Month: Adam's Parachute
Second, the hackle on a parachute dry fly looks like the legs of an insect when viewed from the bottom. As an adult insect emerges from its nymphal body, it extends its legs outward to support its weight on the surface tension of the water. As it continues to crawl out of its shuck, it places more weight on its legs until it's free from the shuck. As the shuck floats away, the adult insect dries its wings and eventually flies away. Only during the wing drying phase of this emergence does a standard dry fly look more natural from below than a parachute dry fly.
Again, when the female returns to the water to lay eggs, its wings often get caught by the surface tension of the water and begin to absorb water. The female will spread her legs out to provide support for her body as she dumps her ballast of eggs and tries to rise above the water to fly away. They are rarely successful in flying away, but their legs and wings remain splayed out on the surface as they expire and float downstream. From the bottom, this also looks a lot like a parachute dry fly.
Finally, the post type wing of a parachute dry fly is easy for the fisherman to see. This is very important during heavy hatches and heavy spinner falls. If your fly looks exactly like all the other flies on the water, it's often lost in the crowd and missed strikes are the result. That's a good reason to use a visible post on your parachute flies.