In deafult game of Minecraft, without mods, you can ride horses and pics but..you can?t ride SPIDERS!
Rideable Spiders 1.7.2 is a mod that allows us to use another animal of the game, as a traveling companion, in this case spiders. The system is very similar to the horses, you will be able to feed the spider and even make armor for them, whether leather, iron, gold or diamond armor.

Detail and Download here : Rideable Spiders Mod

Homepage: Mods for Minecraft