Ants were once men and made their living by tilling the soil. But, not content with the results of their own work, they were always casting longing eyes upon the crops and fruits of their neighbours, which they stole, whenever they got the chance, and added to their own store. At last their covetousness made Jupiter so angry that he changed them into Ants. But, though their forms were changed, their nature remained the same: and so, to this day, they go about among the cornfields and gather the fruits of others' labour, and store them up for their own use.
You may punish a thief, but his bent remains.