No worms in tequila. That is Mezcal. Both are made from Agave, but tequila is only made in certain districts in Mexico, and only using the Weber Blue Agave plant. Anything else is considered mezcal.
The worm is a parasite that feeds on peyote cactus, so is thought to enhance the intoxicant effects of the alcohol.
It is like champagne. Real champagne is only made in Champagne County in France. Anything else is considered sparkling wine.
The main difference in these is there are strict quality standards on the ingredients and the distilling process. Therefore, no worm impurities in tequila.