Adjust the weight

John Kitto, A Cyclopedia of Biblical Literature, Vol II, New York, Mark H. Newman, 1846.

Indeed, the most remarkable of all proofs of animal intelligence is to be found in the larvae of the watter-moths, which get into straws, and adjust the weight of their cases so that it can always float : when too heavy they add a piece of strawe or wood, and when too lioght a bit of gravel..