Is the presence of this source of sap fortuitous?
Or is it the result of deliberate choice on the part of the larva?
I incline towards the second alternative, so repeatedly was the presence of a root verified, at least when my search was skilfully conducted.
Yes, the Cigale, digging its chamber, the nucleus of the future shaft, seeks out the immediate neighbourhood of a small living root; it lays bare a certain portion, which forms part of the wall, without projecting.

This living spot in the wall is the fountain where the supply of moisture is renewed.

When its reservoir is exhausted by the conversion of dry dust into mud the miner descends to its chamber, thrusts its proboscis into the root, and drinks deep from the vat built into the wall.

Its organs well filled, it re-ascends.

It resumes work, damping the hard soil the better to remove it with its talons, reducing the debris to mud, in order to pack it tightly around it and obtain a free passage.