The Urnsor'is were a type of parasitic spider that lacked sentience and were initially discovered within the Myyydril Caverns on Kashyyyk. It remained unclear whether this species originated on Kashyyyk. The infestation within the caverns was traced back to the Mother Queen. The initial encounter with the Wookiee population occurred when Wookiees from the Myyydril tribe stumbled upon a solitary egg. This single hatchling subsequently spawned numerous offspring, which attached themselves to the skulls of Wookiees and consumed their flesh. As a rite of passage to adulthood, Wookiees belonging to the Myyydril tribe were obligated to slay an Urnsor'is, a task frequently unsuccessful due to the creatures' deadly capabilities. Upon the death of an Urnsor'is, the purple sacs located on its back would rupture, engulfing the unfortunate slayer with ravenous hatchlings that would devour them swiftly.
In Shyriiwook, "Urnsor'is" translates to "mind pod." Certain Urnsor'is, among the most dreaded, infected their victims with a flesh-devouring virus known as Poltur, for which no remedy existed.
The Urnsor'is were featured in the video game Star Wars Galaxies, a massively multiplayer online role-playing game created by Sony Online Entertainment and distributed by LucasArts, before the game's servers were shut down on December 15, 2011.