Definitions for caddiswormˈkæd ɪsˌwɜrm
Random House Webster's College Dictionary
the aquatic larva of a caddisfly, having an armored head and a pair of abdominal hooks, and typically living in a case built from sand or plant debris.
Origin of caddisworm:
1615–25; caddis (perh. pl., taken as sing., of caddy, dim. of cad larva, ghost) +worm
larva of the caddis fly; constructs a case of silk covered with sand or plant debris