Megarachnid

The Megarachnids are a race of sapient insectoids native to the planet Murder.

Biology
The Megarachnids largely resemble giant spiders, possessing four limbs for locomotion and four more for attack and defence. Their limbs terminated in sword-like talons comprised of what appears to be an organic metal and were capable of cleaving through Space Marine armour with ease. Their bodies are segmented and covered in an armoured carapace. They possess no eyes but their other senses are heightened significantly to compensate for their blindness. There also exists a flying sub-species of Megarachnid which more closely resembled wasps rather than spiders.

History
The Megarachnids are believed to have once ruled an interstellar empire, until they were bested in a war against an alliance of Humans and Kinebrach known as the Interex. After losing the war, the Megarachnids were deprived of all space-worthy vessels and isolated back on their homeworld. Rather than eradicate them, the Interex instead put into place a series of measures to ensure they could not leave Murder again, nor would anyone accidentally travel there.

Near the end of the Great Crusade, the Imperium of Man discovered Murder, promptly ignoring the Interex's warnings and went to war with the Megarachnids as part of their campaign to exterminate all non-Human life in the galaxy. Within six months, the Megarachnids were driven to the brink of extinction. However, the remnants of their species were spared when the Interex intervened, leading to the Imperium focusing their efforts against them. After this point, the Imperium became divided by the outbreak of the Horus Heresy, a galactic civil war between Imperial loyalists and Chaos worshippers. The fate of the Megarachnids remains unknown.

Technology
Megarachnid technology is primarily organic in nature. At least one Space Marine admitted to looking at a Megarachnid warrior and struggling to discern where its body ended and weapons began. On Murder, the Megarachnids created large tree-like formations 'grown' from a stone-like substance coating their planet's surface. These formations functioned as organic jamming devices, interfering with communications and drop-pod telemetry, as well as even manipulating Murder's weather to suit the Megarachnids.

As the Megarachnids infested at least eight systems before the Interex drove them back to Murder, they likely would have utilised organic spaceships to have established themselves, although they may have possessed more traditional technology before their defeat and exile.