Many species of caddis larva build a protective covering of fine gravel or debris to protect them in this stage.The larva is a bottom dwelling non-swimming stage of the insect.

• 很多的caddis larva会利用水中的沙砾保护自身（我的理解），larva阶段是（昆虫）在水底孵化时不会游泳的时期。