Mezcal is famous for the dead agave worm rolling around at the bottom of the bottle. The alcoholic strength of the contents is proved by the state of preservation of the worm, which is considered a powerful aphrodisiac for Zapotecan Indians. Alas, like most aphrodisiacs, it's all hype and the worm is really just a marketing gimmick.
The worm is usually soaked in pure alcohol before being added to the bottle of mezcal to preserve the worm, some say the worm changes the taste of the drink.
Another variety of worm added to Mezacl is actually the larva of a weevil which can cause a great amount of damage to maguey crops, the damage is caused a bacteria rather than the weevil its self.