Use two types of material

W. Wright RobinsonAnimal Architects, How Spiders and Others Siklmakers Build  Their Amazing Homes, Woodbridge ( Ct), Blackbird Press, 1999, p. 52-53.

Portable homes

The caddisworm’s underwater home is made with silk threads that herden on contact with water. Many of the other materials these builders use are similar to those used by their relatives, the bagworm caterpillars. Both groupe of builders often add leaves twigs, and other plants parts to their silk.

The caddisworms, however, use two types of material that their relatives don’t use : tiny sand grains and pieces of gravel. A home built with thse small stones is much easier to move around in water then on land.. This a because the buoyancy of water makes the stones lighter.

The portable, tube-lik homes of caddisworms have many different shapes and sizes. They may be long and narrow or short and fat. The walls of the tube may be round, square, or triangle shaped. Some of these animal’s homes are straight tubes. Others are curved, and a few coiled, like a snail shell.