Bengali snake charmers used a number of species of snake including the most popular 'Jait' or cobra. Upon capture, venemous snakes would have their fangs removed, with the poison bag carefully preserved. This would reach high prices in local markets where Hindu physicians would purchase venom for use in the treatment of disease. Snake charmers would feed their snakes on fish, frogs and mice. Their charges would rarely live for more than six months in captivity. The snakes were used during the Manasa Devi festival, held in July or August, when priests would make them crawl in front of the idol during ceremonies.
Source: British Library (bl.uk)