Web Spinners are giant spiders mutated to great size by a primary t-Virus infection. Ironically, although called a "Web Spinner", they have evolved beyond the need for a web, preferring to directly chase and attack their prey. The Web Spinners encountered by Jill in the Clock Tower were much more akin to the Black Tiger, as they had redeveloped the ability to create a web and trap their victims.
The Web Spinners were created as part of the initial experiment on arthropod-based B.O.W.s. Developed at the Arklay Laboratory, at least some were scheduled to be destroyed prior to the t-Virus outbreak.