Megarachnids

The Megarachnids are a sentient race of xenos resembling giant spiders that resided in the early 31st Millennium on the planet Murder, which was also known as Urisarach and One-Forty-Twenty. An extremely hostile alien species, they were an old enemy of the non-Imperial human Interex civilisation who instead of committing xenocide had exiled the surviving members of the species to the world they called Urisarach as an act of mercy. The Megarachnids were stripped of their interstellar travel capabilities but they retained the ability to build weather control devices that created powerful atmospheric disturbances and interfered with radio communications. These appeared in the shape of large “trees” found across the planet.