Location: You aren't going to like this... it's under you.
Threat Assessment: 5. A big gigantic worm with a beaked mouth filled with snapping tentacles. The main problem is the graboid can sneak up on you since it travels by burrowing at high speeds. Also, the ground provides it a defense against most weapons. While not intelligent it certainly has a learning curve.
Limitations: Doesn't like loud noises. Animal intelligence. Stinks. The last is probably only a limitation to being invited to the better parties.
Personal Note: One of my favorite beasties. Great movie!