They were fierce defenders of their master's crop. They were all very wolf-like, and Wolf was the most vicious of the three.
As a youth living in Buckland, Frodo Baggins often made trips to steal Bamfurlong mushrooms. On the last occasion Farmer Maggot caught Frodo, beat him, and then threatened to have his dogs eat Frodo if the young Hobbit ever trespassed again. He then set the dogs on Frodo, chasing him all the way to the ferry. Although the dogs did him no harm (they were trained to only scare him), the incident so terrified Frodo that even thirty-some years later he quivered at the thought of crossing the old farmer's land.
Portrayal in adaptations
In Peter Jackson's The Fellowship of the Ring, Wolf appears like a crossbreed between a Rottweiler and a Dobermann. He is also seen barking at the Nazgûl riders when they arrive in front of Farmer Maggot's house, then backing up into the house out of fear.