Illustration of caddisworm
caddisworm
noun
cad·dis·worm ˈka-dəs-ˌwərm 
: the larva of a caddis fly that lives in and carries around a silken case covered with bits of debris
Word History
Etymology
probably alteration of obsolete codworm; from the case or tube in which it lives
First Known Use
1622, in the meaning defined above