To imitate/simulate an adult caddis, a CDC & Elk like this:
http://flyanglersonline.com/flytying...010702fotw.php
or an elk hair caddis like this:
http://www.danica.com/flytier/ccrave...air_caddis.jpg

To imitate/simulate an adult mayfly, a Hairwing Dun like this:
http://flyanglersonline.com/flytying...011606fotw.php