The larvae of many caddisflies, Order Trichoptera, make cases of sand or bits of vegetation, arranged variously from fairly random looking to more uniform to very ordered. The larva of each case-making species makes a characteristically shaped case. Caddisfly larvae can be forced to use unusual materials. French artist Hubert Duprat induces caddisfly larvae to build jewelry with gold and precious and semiprecious stones. (See Cabinet Magazine Online - Trichopterae)
The larvae eventually seal the case (5) and pupate under water. When mature, the pupa chews its way out of the case, swims to the surface and crawls onto a rock, where the winged adult emerges.
I found these pupal caseswith their surprisingly square cross sectionattached to a log a few dozen feet from the shore of the Dungeness River in Sequim, WA, just south of Railroad Bridge Park, on 04 01 2008. The larger case measured about 12 mm in length and 1 - 2 mm on a side.
One pupa had a hole in the side, the other was intact. Both were dry and very hard.
The montage shows all four sides of the larger pupal case.
The family Brachycentridae includes of 37 North American species 33 of which are in two genera, Brachycentrus and Micrasema.