hi A. !
i have 5 kids - the 1st 2 were incredibly sweet & mellow and the constant victims of bullies and biters. my 1st son was 11 mos old when a playmate bit him so hard it bled and it started my baby's 1st nursing strike. it was quite a harrowing experience and it cost me and the mom our friendship b/c i didn't think she disciplined him appropriately. (she did nothing but tell him it wasn't nice as she felt 1 was too young for a time out or isolating him or leaving the playdate - i felt at the least she should have removed him from the imm room and given him a stern talking to, or possibly ended the playdate imm to show him when he bites, he has to leave...)
then i had my next two 15 mos apart and guess what? they were rambunctious, rowdy little biters !! they have never ever bitten another child outside our family, but it just seems to be part of an instinct to be a 'biter'. i know i was one and still get the urge sometimes as an adult ! when i see an adorable kitten or animal or even my own babies, i just get this urge to nibble them. and when i get very angry, i feel my jaw clench up and i just want to bite something in frustration.
so it helped me to understand my kids to feel that way myself. my little girl is 2 and my son is 3 and she is more like me, she likes to bite things that she adores. we have a 6 mo baby and i have to watch her like a hawk b/c when he coos and gigles at her, she just wants to eat him up. she bit him on the finger once, when he was about 3 mos and his screams of surprise and pain really shocked and scared her.
my son got over it pretty quickly, it was just more of a passing phase for him. for him, he wanted to do it when angry or frustrated. during his phase, i redirected his urges to an inanimate object. i found a cpl things i thought would have a very satisfying texture to bite (for him what worked best were these very heavy but soft rubber toy lizards we have) and i kept them close by at all times. when i'd see him getting riled up, i'd imm start reminding him, 'we don't bite ppl, go get your lizard. are you angry? do you need your lizard? where's your lizard?' constantly and for a few days i watched his every move to be there to redirect him. it was funny, a few times when he'd get overwhelmed and the lizards weren't at hand, he'd lunge at the couch like a shark and chomp it ! he's 3 now and hasn't needed to bite anything at all since he was 2.
my daughter is a diff story - it seems to be more of a true oral fixation w/ her and she still very much puts everything that can fit in her mouth in there, too. i've redirected the biting in anger by giving swift and stern consequences -she doesn't do that anymore - esp after biting the new baby - and yes, i did bite her back to show her how it felt and i think that's what stopped that habit, much as it goes against my parenting philosophy ! she continues to have the urge to bite when she sees an adorable baby human or animal or even doll. instead of using the biting object i introduced, she bites her own hand now. it's kind of disconcerting to see, but she hasn't bitten any of her sibs since the baby (3.5 mos now) so it seems to work and she's not biting hard enough to hurt herself.
after having 2 such sweet and mellow kids, it was very difficult for me to have biters and all the negative stigma that goes along w/ that. try not to categorize your child or treat them like they are bad - you want to realize it's an oral fixation phase and while it is aggressive, it's a normal urge they have gotten stuck in and they need help redirecting it, not just punishment for something they can't help. be sure to tell them it's the biting you don't like, not them. they are not naughty, they are just doing a naughty thing.
if you do decide to bite your child back, don't do it while angry. i gave my daughter a time out 1st. once we had both calmed down, i told her she really hurt the baby and asked how she felt to hear him scream and cry like that. i told her she doesn't know how it hurts when she bites and i want to show her. i took her arm and slowly but firmly bit down on the fleshy part. i didn't do it hard enough to actually hurt, only enough to show her the pressure and potential. just feeling caught and helpless seemed to make her really realize what she'd been doing, she hated it and that's when she quit biting anyone else.
good luck and let us know what works, i'm always stockpiling new tips in case the baby decides to bite, too !