Cave Spider

The Blue Spider is a hostile mob that it is believed will be introduced in Minecraft Beta 1.8. It is a spider with a blue retextured skin and is presumably stronger than its dark brown brethren. Blue spiders are much more rare than regular spiders. When bitten by a blue spider, your health gradually decreases. Blue spiders can only be found in Abandoned Mine Shafts, which will also be introduced in 1.8.

Trivia

 * It was originally going to be called a tree spider according to Jeb, but that wouldn't make any sense due to it spawning in mine shafts.