Caddis have three stages: larvae (free, case-building or net spinning), pupae, and adults. You should imitate all, including emergers which can bring explosive action.
During my years on the Little Lehigh I found them unimportant. The prevalent ones were Black Caddis. I never saw one in the water. I assume they crawled in and out. (rgr)
Hydropsyche alternant, Spotted Sedge or Tan Caddis
Emerges from late afternoon into early evening during the summer into early autumn. Sizes 14-22.
Rhycophila abosalis, Olive Sedge
Emerges in the morning, continuing into early evening during the summer into autumn. Sizes 14-22.