Not actually found in tequila but rather in it's cheaper cousin, mescal, it's said that the legendary hallucinogenic properties of the worm are pretty much non-existent. They say it's all a marketing gimmick. There is another use for it though if you eat the worm at a party you will earn the admiration of all your friends! Other than that nothing else happens. But if you eat the worm you probably drank the whole bottle to get it, and that has its own host of side effects.
Besides this, there is superstition surrounding this worm, as some people believe that it brings good fortune and strength to the lucky person who finds it in his or her glass. Be that as it may, worm or not, it is still great to celebrate with an agave-based spirit, so just gather your friends and start drinking copious amounts of it and then you can search for the tequila worm.