Dire weasels grow to be up to 10 feet long and can reach a weight of 700 pounds.

Dire weasels stalk their prey in the dark and then leap on it, biting and clawing.
Attach (Ex): A dire weasel that hits with its bite attack latches onto the opponent?s body with its powerful jaws. An attached dire weasel loses its Dexterity bonus to AC and thus has an AC of 12. An attached dire weasel can be struck with a weapon or grappled itself. To remove an attached dire weasel through grappling, the opponent must achieve a pin against the creature.
Blood Drain (Ex): A dire weasel drains blood for 1d4 points of Consitution damage each round it remains attached.
SEE WIKIPEDIA ENTRY:

• Weasel
  
• Ferret
  

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System Reference Document -> List of Creatures (SRD)