The best example I can give (using pictures I already have) is that the sword feathers have fibers on just one side and are reminiscent of a sword in their appearance. While the 'Herl' are the long fibers 2.5 - 4" found along the quill of an eyed tail feather.
The tail on this Light Spruce is made from Sword fibers, they were only about 1" total length before I tied them in.
The long fibers that make up the under wing on this Golden Witch are herl fibers.
It has been forever since I tied a Zug Bug but I believe you need them for the tail. If this is true in a pinch I would use what I had but if I remember correctly the pattern calls for sword fibers. As you can see they are much more iridescent than the regular herl fibers and that I believe is why they are used on the nymph.
I had just tied these about 2 weeks ago and had the pictures handy, here you can see both for comparison as well as on the streamer version above. The tail is sword while the front portion of the body is made of herls wound around the hook; much brighter green the sword feathers.
Ard
