Caddisflies

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The larvae of some caddisflies (Trichoptera: Helicopsychidae) construct coiled cases which look so much like snail shells as to be readily mistaken. One species was originally described as a mollusc! The trichopteran cases are right-coiled, moderately spired, without banding patterns and often made of dark sand grains. They occur in both running and still but not in saline waters. Close inspection of the case will show whether it is a secreted shell (snail) or cemented from sand grains (Helicopsychidae). If the whole animal is present identification to mollusc or insect is straightforward, based on obvious differences in body form.