Porcupine guard hairs are sold commercially as a substitute for stripped feather quills, used for quill body mayfly patterns.
http://www.mlwebb.com/fly-tying/imag...medal-1214.jpg

The hollow quills can be used for extended mayfly bodies.
http://www.flyanglersonline.com/flyt...061906fotw.php

Used as stonefly legs and tails on super realistic patterns.
http://www.michigan-sportsman.com/fl...stic_stone.htm