Kumo Desu Ga, Nani Ka? is a Manga/Manhwa/Manhua in (English/Raw) language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

In another world, the Hero and the Demon King continued to oppose each other. As their great magic collided, the explosion crossed over worlds and destroyed a classroom full of high school students. The victims who died in that explosion will be reincarnated in that alternate world. Our heroine, who has the lowest standing in the class, was reincarnated into a spider.She nevertheless faces this challenge head-on with great determination, and adapts to it surprisingly quickly. This is the story of how our protagonist, who was reborn as a weak spider monster, does whatever needed to survive.