What materials do caddisfly larvae use to make their cases?

Caddisfly larvae utilize silk produced from glands on their lower lip to construct protective, tubular cases. To provide additional rigidity and protection, they incorporate various materials into these silk structures, most commonly sand grains or vegetable debris.1

These cases are typically open at both ends, allowing the larvae to pull them along as they move and to circulate water for respiration. Before pupating, the larvae attach their cases to solid objects and seal the ends, often using the case itself as a cocoon.1