The impaler colony is an antiquated zerg structure created by the Overmind millennia before the Great War. Its successor was the now-defunct sunken colony. Attacking with subterranean tentacles, its attack is slow, but does incredible damage. At least three impaler colonies survived on Marek V.
During the Second Great War, Ryloth's Brood came under assault by the Dominion's Prometheus Company. Kerrigan sent hydralisks to obtain the essence of the impaler colonies, which was used to allow the hydralisks to morph into impalers and destroy the terran forces.
Three impaler colonies are encountered in the hydralisk evolution mission. The impaler colony's tentacle attacks are identified as a crosshair, and when emerging damage nearby units. Moving units away from the crosshair before the tentacle emerges will avoid damage. When the three impaler colonies are killed and their essence collected, the hydralisks unlock the ability to morph into impalers and the mission continues.