The Pararachnids were a race of space-borne swarming organisms. They would sweep across a planet, leaving it uninhabitable.
Pararachnoids had many legs, antennae, and wings. The Breeder Male had segmented eyes on extensible stalks.
In Peri's far future, the Pararachnoids swarmed over Earth and left it in ruins. They left the planet, leaving behind their weak and crippled. Years later, the Sixth Doctor and Peri landed on Earth when the surviving humans were living underground. The Doctor and one of the humans, Kimo Ani, were captured by the Pararachnoids. The Doctor used his knowledge of the Pararachnoids' sense of smell to escape. They then stopped the Pararachnoids in their attack on the surviving humans. (PROSE: Moon Graffiti)