our older female, Priscilla, almost never bites and if she does, like you said, it is a nibble. However, when she has been (and is now) she bites if I try to hold her from climbing on me or try to pick her up when she does not want to be messed with. Normally she will run to me as soon as I open the cage door, but when pregnant, she sits back nd will not come to me unless I reach to her and let her climb on me. She has bit me a couple of times and drawn blood.