From Tolkien Gateway

The Wormwardens was a new order of knighthood established by Farmer Giles after he had become King Ægidius Draconarius. Their ensign was a dragon.

When Farmer Giles had forced the dragon Chrysophylax to carry a portion of his hoard back to the village of Ham, he needed helpers to guard the worm along the way. Initially he used six servants of the knights who had come with him to find the dragon (but who had been killed or forced to flee when the dragon attacked). Along the way though Giles began to think big thoughts and when they reached the first village on their return he chose a dozen likely lads to join his throng.

As Giles rose to become a king each of the twelve likely lads became a captain of Giles' men-at-arms. Eventually the order of the Wormwardens was formed with the twelve likely lads (now grown) becoming the senior members.[1]