The uninitiated may think that some bottles of tequila have worms in the bottom, but experienced tequila-drinkers know that it's actually mezcal, a similar Mexican liquor, that features a wormy surprise at the bottom of the bottle. When it comes to the effects you'll feel after eating the worm, however, opinions vary.
Tequila vs. Mezcal
Both tequila and mezcal are made from distilling the fermented juice of the agave plant. By law, only liquor distilled from the blue agave and produced in designated areas can be classified as tequila. Mezcal, on the other hand, can be produced in any region of Mexico, and can be made from any species of agave, not just blue agave. As a result, Mexican mezcal producers are not subject to the stringent regulations that govern the production of tequila.
When a bottle of mezcal contains a worm, the mezcal is described as being con gusano, or "with worm" in Spanish. The worm, however, isn't actually a worm, but the larva of one of two different types of moths that live on the agave plant. Although the reason behind the addition of the worm is not verified, one theory is that the worm is a guarantee of high proof; if the worm remains preserved within the bottle, this proves to the customer that the alcohol percentage is high enough to preserve it. Worms are not included in better-quality mezcal.
History of the Worm
According to the Straight Dope website, mezcal maker Jacobo Lozano Paez discovered a moth larvae in a batch of mezcal in 1950, and thought the presence of the creature actually improved its taste. This gave him the idea to place a worm in each bottle of his mezcal as a marketing strategy to set his product apart from others. Over time, the worm became accepted by consumers, and other mezcal manufacturers also added worms to their product. In addition to being a marketing gimmick, jokes Straight Dope writer Cecil Adams, perhaps it was just a ploy to "get the gringos to eat worms."
Consuming the Worm
One of the urban legends surrounding the worm in mezcal is that the worm is so saturated in liquor that eating it causes a hallucinogenic reaction similar to that of peyote. This is likely one of the reasons why eating the worm remains a rite of passage to test the drinker's machismo. However, this particular piece of folklore has no truth to it; eating the worm will not give you hallucinations. One reason for this tall tale could simply result from the fact that the mezcal drinker is probably already highly inebriated by the time the worm is consumed, and may be unable to differentiate between hallucinations and extreme drunkenness.