for the most part they are good. there are a couple that are not. i had a link that i was going to give you, but can not find it now. the bad one i remember is pretty easily recognized. its body is red from tip to top, and along each side are white hairs. they are only bad due to the size they get, and can become predatory, plus if you ever touch one of those hairs. ouch!!
HTH,
G~