Among the many specimens that Dr. Arzt collected on the island was a female Medusa spider, Latrodectus regina. When, on the twenty-fourth day after the crash, Nikki approached Arzt about helping her try to locate her missing bag with his knowledge of trajectories, she examined his Medusa spider specimen. Arzt proceded to explain that the pheromones of the female Medusa spider were strong enough to quickly attract all the male Medusas in quite a large radius.
After Arzt's death at The Black Rock, Nikki kept the Medusa spider, along with several of his other specimens. When on the eighty-first day of their time on the island, Nikki realized that Paulo had been keeping the diamonds they stole from her, she tossed the Medusa at him, causing it to bite him, explaining that Arzt told her that, just as the mythological Medusa could turn a man to stone with one look, the Medusa spider was capable of paralyzing a human being for eight hours, mimicking death, which would have given her long enough to take the diamonds for herself and exact her revenge on Paulo. However, the pheromones from the female she used to paralyze Paulo attracted several male spiders, one of which bit Nikki on the leg. The death-like paralysis that the spiders' venom caused resulted in the two of them being buried alive.
During one of the podcasts,the writers of the show confirmed that The Man in Black took form of the spiders