Fasten together

Eilen MayoThe Story of Living Things and their Evolution, Londres, The Waverley Book, 1948,
p. 206.

The grubs of the Caddis-fly fasten together bits of wood, or, small shells or stones, to form long tubes in which they live. When they want to move or feed, they thrust out the fore part of their bodies. When at rest, they are almost invisible even to  the hungriest fish.