As it digs and advances the larva waters the powdery debris and converts it into a paste, which is immediately applied to the walls by the pressure of the abdomen.

Aridity is followed by plasticity.

The mud thus obtained penetrates the interstices of the rough soil; the more liquid portion enters the substance of the soil by infiltration; the remainder becomes tightly packed and fills up the inequalities of the walls.

Thus the insect obtains an empty tunnel, with no loose waste, as all the loosened soil is utilised on the spot, converted into a mortar which is more compact and homogeneous than the soil through which the shaft is driven.
Thus the larva works in the midst of a coating of mud, which is the cause of its dirtiness, so astonishing when we see it issue from an excessively dry soil.

The perfect insect, although henceforth liberated from the work of a sapper and miner, does not entirely abandon the use of urine as a weapon, employing it as a means of defence.