Cave Spider

The Blue Spider is a hostile mob introduced in Minecraft Beta 1.8. It is a spider with a blue retextured skin and is presumably stronger than its black brethren. Details are limited to a low-res Android screenshot and the fact that it will have its own unique mob spawner. It is found near abandoned mine shafts and can poison the player, turning the health bar green and emptying it at an alarming rate. The player will also be subject to vomiting during this time.

Link for the twitpic photo of the spider is here