Hymenolepis infection (hymenolepiasis) is caused by one of the two species of tapeworm, Hymenolepis nana or Hymenolepis diminuta. Hymenolepis nana infections are much more common than Hymenolepis diminuta infections in humans, because in addition to being spread by insects, the disease can be spread directly from person to person by eggs in feces. Humans and other animals become infected when they intentionally or unintentionally eat material contaminated by insects. In an infected person, it is possible for the worm’s entire life-cycle to be completed in the bowel, so infection can persist for years.