Phase spider

Phase spiders are ethereal beings. They step across the planes of Outland to hunt the unwary. Phase spiders are a type of spider native to Outland, and make their home in the Twisting Nether. They often attack in clusters.

Speculation
Scholars who have studied the Burning Legion speculate that the aranasi are the remnants of a forgotten race on a world long ago conquered by the armies of Sargeras. Due to Phase Spider Mandible that drops from Sael'orn and the presence of Phase Spiders in the Assault on Violet Hold, it is possible that the forgotten race was named phase spider.