What does their worm will not die mean?
There actually was the discovery of Devil worms, which can withstand a tremendous amount of heat and pressure. http://news.nationalgeographic.com/news/2011/06/110601-deepest-worm-earth-devil-science-animals-life/
Some scholars teach that the worms are symbolic of the regrets one will have in Hell, but I understand these as literal worms similar in the sames species as Devil worms. Not only does Jesus in Mark 9:44-48 refer to the worms that dieth not three times, but they are also mentioned in Isaiah. In addition Satan is described as having a“worm that dieth not” above and below him. Hell is a place of fire and also of these gross, disgusting devil worms that symbolize the horrors of death itself. With such a horrid description of hell one would want to make sure that they do not end up there. You need to read my Bible:s Message of Hope to make sure your know Jesus as your personal savior and that heaven is going to be your eternal home.