Spider Riders

Japanese Title: スパイダーライダーズ ～オラクルの勇者たち～

English Title Spider Riders: The Heroes of Oracle

Plot
Eleven year old, Hunter Steel, searches for the legendary inner world by folowing the instrucsion in his grandfather journal. He enters a cave where he finds mysterious manacle that attaches itself to him. A Spider startles Hunter, who falls into a hole to the center of Earth and into the subterranean World of Arachna. There, he discover a small group of elite warriors struggling to survive and to save Arachna from the attack of giant insect mutants. The warriors are still children, each fighting with the help of their own Spiders. They call they self "Spider Riders." In the english series, the ages reduced.

There is a prophecy that says a surface-dweller or Earthen, like Hunter, will bring disaster to the Inner World. Sparkle mention it on beggining  of the TV series. When Princess Sparkle finds out, she says, "I wonder if he will bring doom to us.. or them."