The official GemStone IV encyclopedia.
The Arachne priest's lithe body is covered by heavy silk robes that also cowl most of the facial features. A single visible image of a black spider over a crimson background is clearly emblazoned upon the backside. Draped in their macabre attire, the Arachne priest goes about its zealous duties in worship of Arachne. Upon close inspection, one can make out partial shapes of sigils formed by welts and mutilations on the hands and face.
Arachne priests and priestesses do not wear armor, so they are somewhat easier to hit.
Be wary of hiding or stepping out of the room if it begins to prepare a spell (usually Web); if it cannot target you, then it will resort to casting the Area of Effect version of the spell, which can linger in the room for up to 5 minutes if the priest is not killed.
Arachne priests and priestesses will occasionally enter a state of "shock" after casting a series of spells at one time. This may be a result of attempting to cast a spell while having no mana. This effect stuns the creature, inflicts a minor amount of hitpoint damage, and causes nerve damage:
An Arachne priest appears to be in heavy shock!
... 5 points of damage!
Mild electric jolt sends the Arachne acolyte into spasms.
The Arachne priest is stunned!
Also watch out, sometimes when the priests hit you their weapons will poison you. Usually this is a very strong poison around 40 hp/tick and dissipate usually at 2 per.
Arachne priests and Arachne priestesses are the same creature for the purposes of the Adventurer's Guild bounty hunting. For example, you do not need to exclusively clear out Arachne priests to find a lost child.