The term "Mormon" refers to a follower of the Mormon Christian religion. It gained controversy in the 19th and 20th century because of its polygamy nature. It has since renounced that particular teaching, but it is still a part of their history.
The year before the Bug War began, a group of Mormon extremists settled on the planet Dantana, a world which was cordoned off by the Federation as part of the Arachnid Quarantine Zone. The Mormons, however, disregarded the Federation's warning, and a month later Port Joe Smith was slaughtered by Arachnid warriors.
Some believe that the Bug Meteor launched not long afterwards was retaliation for humans invading Arachnid space.