Spider Riders

Story

TV series by Bee Train — Spring 2006, 26 episodes, Finished.

In this Earth, there exists unknown underground world, the Inner World. In the world, there are braves who fight with large spiders, and they are called “Spider Riders”. According to his grandfather’s diary, a boy, Hunter Steel is traveling around. Meanwhile he happens to enter the Inner World from a pyramid. There, the war between the insect squad that aims at conquest of the Inner World and Spider Riders continues. Oracle, the fairly of the Inner World, summons Hunter because he thinks Hunter will be the messiah of the world.

Synopsis via AniList (English).