caseworm n [OED3 caseworm n. 1 c1565→; from the protective case constructed by many species] Cf casefly n

The larva of a caddis fly (order Trichoptera), often used as bait. Also called hellgrammite n 4, pennywinkle n 3, periwinkle n2 2, reedamite n, rock bait n, rock-roller n 1, rock worm n 1, sandstoodle n, stick bait n, stick bug n 3, stick worm n 1

1846 (1850) Banvard Young Observers 3.27, I will now tell you all that I know about these novel little water-men. They are called case-worms, straw-worms and caddis-worms. They possess the power of spinning threads in the water. 1882 Lancaster Daily Intelligencer (PA) 10 June 1/4, The curious little worms, enclosed in a gravel-covered follicle, which you . . recently observed in a spring in Franklin county, are commonly called “caddice-worms” or “case-worms.” 1884 IL Bd. Fish Comms. Report 114, The second group [of common sunfish] . . was peculiar in the number of tetradecapod Crustacea and case-worms taken, and especially in the amount of vegetation eaten. 1899 ME Dept. Ag. Annual Rept. for 1898 122, We received some caddice fly larvæ . . from Mr. William Miller, manager of the Mt. Desert Nurseries, Bar Harbor, Maine. Mr. Miller stated regarding them: “That they have practically eaten up our hardy water lilies. . . As soon as we discovered what was destroying them, we took steps to eradicate them. . . The first three days one man gathered each day, about 3 gallons of the case worms.” 1913 Woodland Daily Democrat (CA) 20 [Mar 3]/3, They state that there is at present plenty of salmonflies and caseworms. 1926 Essig Insects N. Amer. 172 West, The larvae are . . known as case worms, caddis worms, or to many country boys as fish bait. 1934 Herald–Jrl. (Logan UT) 9 Jan 2/1, A remarkable group of insects in our local rivers and ponds are the Caddis worms, or case worms (wrongly called rock rollers) which are the immature stages of the Caddis flies. 1949 Detroit Free Press (MI) 16 Jan sec C 4/6, “Wrigglers” . . are topnotch bluegill bait. Caddis fly larvae or “case worms” often called reedamites are good too. 1963 San Francisco Examiner (CA) 6 May sec IV 7/1, Another top bait is the case worm, which is the larva of the caddis fly. It builds a case, or shell of fine gravel around its body for protection. 1991 Sacramento Bee (CA) 21 July sec A 16/1, You have trout and salmon flies, hellgrammites, case worms—they all hatch in the river. 2008 in 2020 DARE File—Internet swCA, I’ve fished with helgramites, although we usually called them case worms. They are a pain to get but wow are they worth it!