From WoWWiki

Little is known about the sand worms. They are worm-like creatures with burrowing claws growing from the upper body. These enable the beasts to dig through most kinds of soil with frightening speed, often surprising unwary pray by bursting up through the ground beneath the creature and killing it with its sharp beak-like mouth. You can spot where they are because rocks/the ground move above them.

The massive worm Ouro was believed to be the only one in existence, but smaller versions of the worms can be found in Outland. They are found in Hellfire Peninsula, Terokkar Forest and Blade's Edge Mountains. The Hellfire variant is called burrowers, the Blade's Edge variant is known as crust bursters, and the Terokkar strain is called bone worms.

Whilst underground, sand worms cannot be targeted. This means that you will most likely not get the opening move if you run into one - no ambush, pounce, charge, or uninterrupted starfire/shadowbolt/fireball, since you'll already be in combat if you can target it.

Young Burrowers are unable to tunnel, and also seem to lack the characteristic claws.

Noteworthy sand worms

• Fulgorge
• Hai'shulud
• Ouro