My dog is a male terrier mix. About 4 years old. I adopted him from the humane society about 2 years ago. If somebody comes over to my house that he does not know and they try to pet him, he bites them and just pretty much goes crazy. But before the person tries to pet him, he is fine and wagging his tail like nothing is wrong. But when the person tries to pet him, he bites. Does anybody know why he does this??
Thank You!!!

Perhaps fear? I would keep him in a crate or another room when you have guests over. If someone were to report the bites, it could end badly for your pup.

you could also tell the people to not pet him or look/speak to him and have him lay down in a diffrent room for a little bit. Then let him in and let him go to them and smell them. Then see what happens. But i agree with the other comment...could be very bad if he gets reported...crating could be the only answer?

Has he been doing that for 2 years or did it just start? If it is a recent development, a vet visit may be in order to make sure that he doesn't have a health issue that you don't know about that may make him scared or nervous about people touching him. For example, if he has a painful ear infection, he may bite when someone reaches toward his head to pet him.

Sucker training! LOL Honestly you can do this and it will help him be less sensitive. Set him up for this by having someone you know he has tried to bite, and prearrange for them to have treats in their hand at your door. Have them throw him a treat,let him sniff or eat it, then have them try and excite him by calling his name, throw a treat again,and then see how his demeanor is. Try and see if they hand him one{have them wear leathr gloves} so they are not hurt though!!! Repitition of this will make you dore willing to accept that compnay is ok for you,but he will see the outside world as he needs to protect! Try,try till he has it down!