The first sign of danger

Leslie JackmanObserving the Countryside and Seashore, Londres, Bloomsburry Books, 1993, p. 74.

Most pond coutain caddisfly larvae and these little creatures live in tubes that they have constructed and lined with silk to which they attach a wide variety of small objects, some using the shell of small  snails, others tiny fragments of sturated wood, while others prefer fragments of chewed-off plant stem. Inside these shelters, with only their legs and head protruding they walk around and climb among the submerged plants.  At the first sign of danger they withdrew into the tube.