The Spider Daleks were slightly larger than the Dalek drone, with eight legs. They were more manoeuvreable than standard Daleks, but more vulnerable at their joints. The Thals believed that this design had been abandoned for centuries. Giant-sized versions, known as Striders, were ten times larger than the standard Spider Dalek. (PROSE: War of the Daleks)
Behind the scenes
The Spider Dalek was a new version of Dalek which might have appeared in a proposed revival of Doctor Who developed during the mid-1990s. (A backdoor pilot for the proposed revival appeared as Doctor Who).
The redesign was intended to take full advantage of the then-new technology of CGI, but bore little resemblance to their predecessors. Concept art depicted these creatures as having six-legged, adaptive casings, from which their mutant controller could emerge, wielding claws and lethal weaponry. As these were being designed, a CGI test of the new version of Dalek was leaked to the internet.