Huts of pebbles

Helen Damrosch Tee-VanInsects are where you find them, New York,  Alfred A. Knopf, 1963.

The larvae make  cases of pebbles or live in tubes made of sticks or sand or other materials at hand. Some larvae cases are made of a paper-like silk. Some of the larvae live in swift streams. Sometimes they make little huts of pebbles and bits of debris partly held together by silk.