Talking of Tequila and Mezcal.
Apart from being Polish and a major pain in the ass, I have also the privilege of being Mexican. (my dad was mexican, my mom's polish)
Anyways, the whole peyote eating worms in Mezcal is utter BS. Yes, ladies and gents, you heard it well.
The worms that float at the bottle of your mezcal bottle are Maguey worms, which are called like that because of the fact they live and feed on Maguey trees (sap). I lived in Mexico 10 years, I've seen the trees, I've seen the little buggers sucking the sap, I've drunk quite a lot of Mezcal.
Mezcal is derived from agaves, yes, but another type than Tequila. Tequila, traditionally, is brewed from blue agaves, which are nowadays very rare because of the tequila industry boom. Hence the second hand tequila like brews (double distillation) that give you a major hangover. Tequila doesn't, believe me. Anyways, even in Mexico Tequila is pretty expensive: 50 bucks a bottle.
The agaves that are used to produce Mezcal are far more common, they're smaller and there's tons of them in Oaxaca, the brewing/distilling process isn't as time consuming as tequila. Generally speaking, Mezcal is considered an "inferior" drink than tequila, it's your basic rotgut, booze.
Theres around 40% alcohol both in Tequila and Mezcal, there's practically no difference between the alcohol "dosage". The worm, also, is purely symbolic. It isn't little psychodelic, peyote-eating organic LSD. I've eaten the thing a couple of times (the worm not peyotl) the thing is full of alcohol so it gives you a special buzz. The effects of getting drunk with mezcal are pretty different from getting hammered with beer.
Anyways, the worm's there as a part of tradition, it means the mexican soil was fertile before the arrival of the Spanish.