This is a bit of an old story, but as this is a new blog I'm going to go ahead and forgive myself.
You've likely seen a caddisfly on a hike or while fishing, you just never knew what they were before now. Caddisflies belong to the order Trichoptera, a small order of holometabolous insects which includes approximately 10,000 species worldwide. The adults resemble small moths with large wings that fold over their backs while at rest. Most species are small (1/4" or less), dull in color, have long, thin antennae, and are active during dusk and night hours.
The larvae and pupae are primarily aquatic and can be found in many freshwater habitats and even some salty. These immature stages resemble grubs or caterpillars. Many species produce silk to construct cases of plant material, small twigs, sand, small rocks and debris. These cases, or cocoons, are used for protection, breathing purposes, and feeding.
Know you know a bit of the taxonomy and life history, check this out:
French artist Herbert Duprat took caddisfly larvae and put them tanks filled with gold and precious gems. The larvae, looking for materials to build their cases, used the glittery, expensive items for their construction, binding it together with silk.
Here's the link: http://collection.fraclorraine.org/collection/show/168?lang=en#
(images from eoearth.com and usc.es)