The esideor are spirits from some of the darkest planes of the shadow lands. They typically appear as massive spiders with a dark black-blue carapace. As the esideor is a powerful spirit they can appear in any number of forms, but seem to prefer spiders with an enlarged abdomen.
A esideor has many spinnerets on its enlarged abdomen - the more spinnerets the more powerful the esideor. From these spinnerets come threads of the Shadow Realms. The esideor can spin these powerful threads into complex weaves and patterns, drawing more power than any other spirit of the shadow lands. Weaving these threads into the proper pattern is difficult and time-consuming.
Most esideor will have hundreds or thousands of spiderlings that follow them around. These spiderlings are not simply smaller or immature versions of a esideor, but a different creature native to their lands. These spiderlings attach themselves as parasites to the host and drink its blood. A small measure of the esideor's power is then transferred to the spiderling. If the spiderling lives long enough for hundreds of feeding they develop a dependence on the power of the esideor and will no longer seek out other esideor.
The spiderlings act not only as scouts and caretakers, while the esideor resides in its hole - feeling the vibrations of spirits along its web, but are the method used by the esideor to take over the physical body of other creatures. The spiderling can attach itself to weaker spirits and dominate them.
No scholar understands why the esideor attacked the realm of fire in concentrated numbers. The esideor will as often fight among themselves as bother with anything outside of their plane. What is known is that thousands of esideor streamed out of their plane and attacked the ifrit. They did not just hunt the ifrit int the Realms of Fire, but hunted them in other lands the ifritii lived. They killed hundreds of thousands of ifritii and enslaved many more.
In time the ifrit freed themselves and hunted the esideor in turn. In a deserved twist, the ifrit either killed or enslaved any esideor outside of their native plane. Those ifrit who went into the plane never returned.