Ants were once men who tilled the soil for a living. However, dissatisfied with their own harvest, they constantly cast longing eyes upon their neighbors' crops and fruits. Whenever an opportunity arose, they would steal these goods and add them to their own stores. Their covetousness eventually angered Jupiter so greatly that he transformed them into ants. Yet, though their form changed, their nature remained the same. To this day, they roam the cornfields, gathering the fruits of others' labor and storing them for their own use.
You may punish a thief, but his bent remains.