(Okay, so this isn't such a short tale, but as I have no better place for it at the moment, here it is.)

There is a story with a Worm that is Ardasir's final heroic deed that appears in Ferdawsi's Shahnama.

The daughter of the poor Haftvad bit into an apple that she found and in it was a little worm. She put it next to her spinning wheel and fed it apples every day until it grew too large for the spindle box. In return for the apple, the worm aided her spinning so that she did more work with greater quality.

So much wealth did the family collect that the local prince tried levying massive taxes. Haftvad and his sons killed the prince, then built a fortress to guard the town. Their power extended until Ardasir, a hero and warrior, took notice and laid seige to the castle.

After several poinant warning (including an arrow in his food), Ardasir retreated to where he met 2 wise men who told him that the worm was Ahriman. Ardasir returned to the city and, by trickery, made it to the worms chamber where they poured molten brass down its throat.

Haftvad and sons were executed and Ardasir leveled the fortress.

Related to: Ahriman.