The vast and fortified appearance of the great purple worm might suggest to some that it has reached the peak of its life cycle, but this isn't the case. Indeed, "worm" is an entomologically inaccurate term for what the the creature actually is: a caterpillar. And like all caterpillars, it must eventually metamorphose.

When a purple worm has grown old and large enough, it begins to burrow deeper and deeper into the heart of the earth, where the rays of the sun could never hope to reach and where even the deepest delvers haven't traversed. There, they curl into a vaguely spherical position and begin the long, slow process of creating a chrysalis around themselves: a massive, iridescent violet shell that protects them as their form shifts. After months on end in a state of suspended animation, the shell finally cracks, and what emerges is a sight of nearly unimaginable beauty and terror: the Violet Greatmoth.

Unlike purple worms, Violet Greatmoths are short-lived and efficient. Rather than spend countless hours aimlessly carving through the solid rock of the Underdark, eating anything in their path, they instead focus solely on reproduction. Since the deep locales in which Violet Greatmoths appear are nigh inaccessible to others, there are few interruptions to their mating process, making it easy to locate and mate with others of their kind. When they do, they leave behind a mass of spherical black eggs suspended within a gelatinous, clear slime. These eventually hatch into new purple worms which will make their way back up through the world, consuming unfortunate creatures endlessly until they too are ready to repeat the cycle.