Megarachnids - Murdering Murder: A company of the Emperor's Children Legion arrived in response to the Blood Angels' distress calls. They made the same mistakes the Blood Angels had made, and had their landing parties scattered by the planet's powerful atmospheric disturbances. While the company took heavy casualties, one landing party led by Captain Saul Tarvitz discovered a large rock-like structure that resembled a dead tree. This "tree" had the bodies of several Blood Angels Space Marines impaled on its many branches with flying variants of the Megarachnids feasting upon the bodies. After destroying the structure, the sky above where the "tree" had been suddenly began to clear of the violent storms that had afflicted the Imperial forces from the beginning. Captain Tarvitz realized that these structures were actually artificial weather control devices that were responsible for Murder's heavy atmospheric turbulence.The Megarachnids immediately went about rebuilding the "tree" and sent hundreds of warriors to slaughter the last few Emperor's Children Astartes remaining. But just as the Space Marines were about to be overwhelmed, a relief force of newly-arrived Luna Wolves Astartes from the Warmaster Horus' own 63rd Expeditionary Fleet began to land through the breach in the atmosphere. The Megarachnids were scattered, and a full-scale assault on the hostile xenos of Murder began in earnest.Ten companies of Luna Wolves, the remnants of the Emperor's Children, tens of thousands of Imperial Army soldiers, and several Legio Mortis Titans proceeded to level entire swathes of the grass stalk forests and destroy every one of the "trees" they encountered, which steadily eroded Murder's atmospheric barrier. The Warmaster Horus, who was commanding the Imperial assault from his flagship in orbit, was very pleased with the progress being made. Some consideration had been paid to initiating a withdrawal from Murder now that a proper landing zone was available to allow an easy extraction of the troops, when an unexpected visitor suddenly arrived.The Primarch Sanguinius came to the world to inspect the dead of his original Blood Angels landing force that had been wiped out early in the campaign. With tears in his eyes Sanguinius asked his brother Horus if he would join him in a campaign of vengeance against the foul xenos. The Warmaster replied: "Yes, let us murder Murder."Adding five of his companies of Blood Angels to the Imperial invasion force, Sanguinius and his forces fought alongside the Warmaster against the aliens. Thousands of Megarachnids poured out of the forests and canyons of Murder in an endless wave. Despite never retreating from the Imperial assault, the Megarachnids only continued to lose ground. By the sixth month of the campaign it seemed the Megarachnids would soon face extinction when a fleet deployed by the Interex arrived in-system to determine who had assaulted their Megarachnids' reservation world. Finding contact with the highly-advanced humans of the Interex to be a more pressing issue that needed to be dealt with, Horus ended the campaign against the xenos of Murder. The Megarachnids had been saved from extinction for a second time by their old enemy. Imperial records do not indicate the final fate of this savage species once the Horus Heresy began.