The Doors of Oerth
The Aranea on the islands are a small offshoot of a small caste of Nerubians from a land in another plane called Kalimdor. They have dwindled in population for the better part of two hundred years, a small enclave found themselves wandering through jungles they did not recognize. Within months of their arrival, their numbers had been cut in half, the largest Spider Lords having been simply eaten by larger predators they could night fight against. Eventually they would establish a small colony and built the Ziggurats surrounding their colonies and webbing is stretched between their trees to watch for intruders. Initially an attempt was made to establish a network of warrens like they had on Kalimdor but far to many of the creatures who attempted to do so disappeared. The practice has long since been abandoned in favor of much safer tree dwellings.
The colony now consists of around two dozen surviving Areana, many of which have turned to the practice of a new form of Illusion magic discovered on the island that seems to come naturally to them. They have made attempts in the past to contact the neighboring villagers but their efforts have been rebuked in the past. One such encounter turned deadly for both sides and started off a wave of attacks the head hunters launched that included many undead. Individually, the Aranea were more powerful then that of the human warriors, but the sheer number of them who seemed to be more then willing to kill themselves in order to destroy the spider creatures was staggering. Eventually the Aranea learned many powerful spells of illusion used to conceal their environs and hide themselves from the prying eyes of the outside world.