The X-Caddis represents a crippled caddis, an adult that has not succesfully emerged from the pupal case. Since caddis normally emerge quickly and do not linger on the surface like mayflies, the only adults readily available to trout during the hatch are pupae and cripples. Trout know the cripples aren't going anywhere, so they focus on them. Cripple patterns such as this are especially effective on clear, slow water where trout can become exceptionally selective.
Abdomen and wing colors are chosen to match the natural insect.
How to Fish
Dress the fly with floatant and use standard dry fly presentations.