 Some animals actively seek to hide by decorating themselves with materials such as twigs , sand , or pieces of shell from their environment , to break up their outlines , to conceal the features of their bodies , and to match their backgrounds . For example , a caddis fly larva builds a decorated case and lives almost entirely inside it ; a decorator crab covers its back with seaweed , sponges and stones . The nymph of the predatory masked bug uses its hind legs and a ' tarsal fan ' to decorate its body with sand or dust . There are two layers of bristles ( trichomes ) over the body . On these , the nymph spreads an inner layer of fine particles and an outer layer of coarser particles . The camouflage may conceal the bug from both predators and prey . 
