To begin with, there is no worm in Tequila. And if you're saying, "Ew, Tequila burns!", then you need to read this and try some good Tequila

NOM (Norma Oficial Mexicana),the Mexican governing agent of tequila dictates that, tequilas distilled from 100% Blue Agave must be labeled 100%. Most of the premium brands are bottled in Mexico. A lot of the tequila produced in the United States is mixed with cane alcohol to produce the cheaper priced 51% Agave Tequilas. 

Types 

Silver - (Plato or Blanco) is not aged & bottled within 60 days. 
Dorado - (Gold) usually just refers to it's caramel coloring. 
Resposado - (Rested) is aged for two months to one year. 
Anejo - (Aged) is aged at least one year, but no more than five years. 
(Tequila has no advantage to longer aging.) 

The Story 

We have the Spaniards to thank for inventing tequila. The Aztecs were making a potable called "Pulque" from fermenting the liquid inside the "maguey". It was illegal to become intoxicated, so only the old, sick and nursing mothers were allowed to drink it. It was also used in religious rituals. The Spaniards who came to the area disliked it. They tried fermenting it and the result became known as "Mezcal." 

Mezcal is the "Mother of Tequila". Mezcal can be made in many varieties from different agave plants, but tequila is made only from the Weber Blue Agave. Closely related to the lily, the Agave is not a cactus. There are over 120 types of agave, but tequila is made from only the Blue Agave. It takes 8 to 12 years to produce a "pina", called so because it looks so much like a pineapple. It grows on the hillsides in the state of Jalisco, which is home to the town of Tequila

The first commercial tequila begins with Jose Cuervo, the first to get rights from the Spanish government to cultivate the Blue Agave and to produce tequila, but Cenobio Sauza was the first to import it to the U.S. 

Producing tequila is an age old art. The jimadores hand cut and carried the heavy pinas and cooked them for three days in stone ovens. It was then ground into tahona, by a big grinding stone powered by animals, and fermented in wood barrels. It was distilled usually in clay pots. 

In the small region that tequila is made, it comprises the majority of the population's income. The laborers, have never really evolved, working as their fathers before them did. The making of it doesn't really differ much from how tequila is made today, except for the modernization of the process. The Blue Agave is still hand processed. The agaveros (agave farmers) have felt deprived in the commercialization. However, there is a change afoot with newer tequilas, Trienta Trienta (or 30 -30) is as an example. Seventeen of the agaveros that have joined together to produce a tequila that is is 100% Blue Agave made in the old traditions.