Kumoko

Kumoko was formerly a female high school student in modern day Japan. She died and reincarnated into the form of a spider.

In her former life, she lived as a shut-in and immersed herself in video games, but now she uses her remarkable mental strength to fight for survival. She uses battle tactics that make up for her low stats with her mastery of agility, spider thread, and poison fangs.

(Source: Official Site)

In just two years, Kumoko became known as "The nightmare of The Labyrinth." She was feared as a man-eating god, and the "children" she left behind became known as "the remnants of the nightmare."
Light novel spoiler:

She is actually a normal spider who was in the classroom when the explosion happened. She got reincarnated with the memories of Hiiro Wakaba as a substitute for the real one.