I posted this a few days ago but there were no replies and it's not getting any better! This evening Benny went to attack Smokey and luckily my hand made it in between and he got me instead! Smokey and hiccup are not enjoying play time the are completely terrified and sit up on mine and my boyfriends shoulders the whole time...but here's a bit more about it: I haven't really been keeping rats for very long, so although I know lots about them from doing research...it's very different when you experience something! I recently took in three adult male rats they are 18 months old. I also have three younger rats who are all around 5 months old (2 boys and one girl). I have seen play fighting before but never have I come across an aggressive rat before - until now. The three new rats are so so sweet to humans and I've not come across any aggression directed towards me, but Benny is really aggressive to the other two The lady I got them from said she never witnessed anything serious just the odd scrap. Benny parades around the free range area puffed up and then if he see's Smokey or Hiccup he chases them and attacks. I have noticed that Smokey in particular is TERRIFIED of Benny, he freezes every time Benny goes near him and screams and freaks out if Benny touches/chases him. Hiccup isn't quite as scared but still isn't keen on Benny. Both Hiccup and Smokey have some deep gouges on their backs from Benny and since Smokey is a rex he gets cut up a bit easier. I've witnessed this behaviour both inside and outside of the cage. I really don't know how to handle this aggression as I've never dealt with it or seen it first hand, any ideas what could be causing this? Could it be due to an environment change? Smokey's scared behaviour suggests to me that is a long-term issue, or can these things happen so suddenly? How do I stop it? I know I can neuter as a last resort, but what do I do when I see Benny going for the other two? Do I intervene and pin him/tell him off or will this just make it worse? Benny really is super sweet towards humans and loves shoulder rides, but if he's aggressive towards his current cage mates I'm never going to be able to introduce him to my three others... Ronnie is so small she'd get eaten!!!The previous owner only had them for 4 months as she took them on from someone else who couldn't look after them any more she also said that they had a pretty empty cage, whereas with me their cage is quite full. I've made sure there are enough hammocks/sputniks/water/food so that no one can guard anything and there is enough space for them to get away from each other, could he being aggressive over the items in the cage? They have never had any direct interaction with any other rats, and apparently the one time they almost did Benny bit someone's foot. Any advice would be really great, I don't know what to do. I feel awful every time I leave the house or go to sleep that someone is going to get hurt! Do I neuter him? What else can I try first?