Hi K.: I had the same problem with my son who just turned 3 on the 11th of October. He was a bad nail biter.... When I was a kid, I used to bite my nails as well and when I did my mom would tell me that a fingernail tree would grow in my tummy and I would have to go to the doctor and they would have to take it out. Well, I know that we all don't agree with things that our own parents have told us but I tried the same thing except I added to it... I kept telling my son that biting his nails was yucky because he had germs under his nails that could make him sick. I then told him about the finger nail tree and that it would even start to come out of his ears and nose and the only way to get rid of it was to have an operation on his tummy. He would ask me a whole bunch of questions about it. It took a bit and his stopped. I would also go weeks without having to cut his nails and that is why I told him the story that I did. I now cut his nails once a week, and since they grow so fast, sometimes twice a week. He looks at me now and says "Mommy, I'm not biting my nails because it is yucky!" It's worth a shot. I know that all parents have different things they come up with to try and solve a problem and for me it worked as a kid and worked on my son as well.
Good Luck. My son is pretty stubborn so if it worked on him it should work on any little one. :)
L. P