The pitvipers of the mines are thick black creatures that can grow to be a width of a foot. Originally from Earth like all flora and fauna, they mutated in the deep tunnels of Mars. They are capable of biting through a frysuit. Not only that, but they have a strong poison that will kill those too weak to resist it, or strengthen the heart of the one being bitten. The poison can't even be sucked out. They burrow into the warmest place that they can find to lay there eggs, most commonly ones belly.