Intriguing study in camouflage

Ellen Mary Stephenson & Charles Samuel Stewart-EvisonAnimal Camouflage,  Londres, A. & C. Black, 1955, p. 68. 

Caddis Larvae

The caddis larvae of ponds and slow-moving streams provide a homely but intriguing study in camouflage. These soft-bodied, edible insects weave for themselves a tube of silk into which they fasten scraps of twig or leaf, tiny shells, pieces of fine gravel, and suchlike materials gathered from the bottom of the pond. They made bite pieces of suitable shape from the living leaves of water plants and weld them into a light, pliable tube with the aid of silk spun in their mouths. The caddis larvae crawl about with only their head end exposed, and at the approach of danger withdraw safe within their portable houses. How deceptive these tubes are be realised from a single example.

Standing on the edge of an artificial pond and looking down its sloping concrete sides scraps of twig were obseeved resting here and there on the slope, or floating at the surface. The water was quite still – yet some of the twigs moved slowly about! These moving twigs were caddis larvae browsing in minute green stuff on the concrete side.