The thorax is divided into three segments, with each segment having a pair of legs. The rest of the body is made of a long, segmented, and flexible abdomen that ends with hook-like 'prolegs'. These 'prolegs' act like drag hooks. The nymph uses these prolegs to pull its tube-like case along the bottom. The nymph can pull itself inside its case quickly.
Some nymphs make hinged trapdoors which they can pull down for protection.
These nymphs use their prolegs to hold the trapdoors in place. As the nymph grows, it either enlarges its tube by adding on pieces at the head-end, or builds another case and discards the old case. If the case is made of stones, bark or twigs, the nymph usually enlarges this case. If the case is made of leaves, grass or silk-like threads, the nymph usually builds a new case because the old case is worn out.