The CFA Cased Caddis Perdigon was designed specifically to replicate caddis casings found on the bottom of most trout streams. These casings get dislodged during highwater events, also known as catastrophic drift. When this occurs these casings make an easy meal. However, caddis casings are present in the water column year round, making this fly a viable option year round. 

Search terms: caddis larva & caddis pupa/emerger (Czech Caddis, Rock Worm, LaFontaine Caddis Emerger).