The in-game WoW creature has the name "nerubian spiderling" in the game files. Although they aren't identified in-game as such, and they have no humanoid section like the nerubian spiderlings in Warcraft III.
This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore.
As they have six legs they could be insects and not spiders. Nerubians might form some sort of symbiotic relation with a variety of non-nerubian insects, carrying them with them even in undeath as seen with crypt lords' use of insects: carrion beetles and locusts.