Spider vessels are creatures carrying many little spiders. They resemble humanoids because they had been humanoids before they were captured and transformed into monstrosities to become vessels for little spiders. During this transformation, they are stripped of their past lives, memories, and wisdom. In the end, they turn into creatures who only care for feeding and protecting the spiders they carry.
Spider vessels are created by evil underground races, cults dedicated to spiders or most insane individuals.