D&Dtools1

A fang-shaped crystal dangles from a loop of finely wrought silver chain in the center of this spiderweb medallion. When the chain is used to wrap the fang scarab around the juncture of a monstrous spider's cephalothorax (head) and abdomen, the creature can hear Lolth's dark whispers in its subconscious. This gives it an instinctive knowledge of what the next moment will bring, which manifests as a +1 insight bonus on attack rolls.

Because the fang scarab is designed for spiders, it's not useful to most adventurers. A nonspider can make a fang scarab function with a successful Use Magic Device check (DC 25), but this also fuses it permanently to its user's neck, near the throat. Nothing short of the wearer's death can then remove it.

Though the fang scarab grants its wearer the same attack bonus that it would to a spider, it also initiates a terrible metamorphosis that changes the wearer into a half-spider abomination over time. When the scarab first attaches itself, the wearer's canine teeth enlarge, and coarse black hair appears on the back of her neck. No further changes occur until she attains levels in the fang of Lolth prestige class.