Mezcal
Mezcal, or mescal, is a distilled alcoholic beverage made from the maguey plant (a form of agave, Agave americana) native to Mexico. The word mezcal comes from Nahuatl mexcalli and it means "oven-cooked agave".
Tequila is a produced from a mezcal made specifically from the blue agave in select regions of the Mexico.
Mezcal and the worm
Not all bottles of mezcal contain a “worm” (actually a the larva of a moth, Hypopta agavis that can infest maguey plants), but if added, it is added during the bottling process. There are conflicting stories as to why such would be added. Some state that it is a marketing ploy. Others state that it is there to prove that the mezcal is fit to drink, and still others state that the larva is there to impart flavour.
Drinking mezcal
In Mexico, mezcal is generally drunk straight, not mixed in a cocktail. There are a couple of rituals associated with it. One is saying "Arriba, abajo, al centro y pa´ dentro", (up, down, center and in) before the first shot. The other involves spilling a small portion onto the ground as an offering to the Mayahuel, the goddess of maguey and the fertility of the earth. While mezcal is generally not mixed with any other liquids, some add salt, or eat lime or orange slices with it.
The most traditional Oaxaca way to drink mezcal is as a shot, with a side plate of fried larvae ground with chili peppers and salt and cut limes. One takes a pinch of the larvae mixture and places it on the tongue, then immediately begins to drink the shot, but slowly. For first-timers, the flavour can be disagreeable, harsh and even cause coughing. It is an acquired taste. It is believed that it can help control diseases such as hypertension and diabetes, and is even an aphrodisiac.