NEED HELP / ADVICE - My Mice have become vicious little killers! NO JOKE!

I really need some advice / help.

I have a group of what I thought was very sweet mice that I have received from several sources: PetSmart / other pet store / a girl breeding them for school project, person that bought too many and snake would not eat them all, etc. They have always been hand friendly, tame and all live together - they are all females!

For years when a mouse died, they would bury the body. I found it somewhat nice and annoying, as I did not always find the body until 'the smell' started, then I would did through the aspen and find the body.

Recently they have started to eat a mouse when it dies, this is new but I have read online that they may do this from time to time. Now we have hit a new step, at least twice in the last few weeks, when an older mouse starts losing weight and is getting older and a little slower - they feel cold and don't wake up quickly, they have been killed by the others and eaten.

I have not been present for either killings, but I did one day stop an attack on a younger mouse. She was waking up and two others started biting her mouth / lower lip, I went over to the tank when I saw a third one going over to them. I have never seen that behaviour before! I took her out, and put her in a separate cage for the night, her mouth had cut and blood on it. The next day she went back in and she was fine, and is still in there today. This occurred back in early January!

Last night I went by the cage before dinner and saw one of the older ones that has been getting thinner walking around slowly and I thought she may need to go into 'protective custody' over night, just to be safe. I came back after dinner - 2 hours and there was almost nothing left of her.

I need help or advice about this blood lust they seem to have, is this normal at all?? They have also started biting me when my hand goes into the tank with or without food, even some that are usually big softies.

---Update---

The largest - by quite a bit too - mouse in my tank was just jumped by four other mice. I heard a squeak I have never heard before and when I pulled them off her her foot is all bloody - but still fully intact. Odd they would attack her she is the "alpha" of the group.

I really don't know what to do!!!!

First of all, when you start noticing a mouse is ill, than it is already very sick. A mouse will do everything it can to appear healthy, even when it's not, because it is a prey animal. For it to be already very thin, cold and slow, it's actually on the edge of dying. So when you leave for even a half an hour and then come back and it's dead, that's normal for mice in that condition...

Mice don't like having a body laying around. They might get sick from it or the smell might attract predators. So they will want to get rid of it by burying or eating it. This is very normal.

It is also normal for them to not want a sick mouse amongst them. They might not be killing it on purpose, they just want to chase the sicky away, but since they can't go anywhere the stress sets the very ill mouse that is on the edge of dying over the edge...

A mouse that is ill, will not be able to be boss any more, the alpha position is only for strong and healthy mice.

The only thing you can do is to keep the sick mouse separate from the others. As I mentioned, when they are thin, cold and slow they are already far along and that means they are also suffering and I'd suggest putting it out of it's misery when it's an old mouse or trying to nurse it back to health if you think it can still make it.

A nursing tank should ideally be a very small one, like a carrier and be in a warm and draught free environment.. The smaller the better, because it won't have to go far for food and water, it can't fall of of anything and it has to be kept as inactive as possible to conserve it's energy for recovering.
The mouse will probably not be able to eat and drink on it's own, so you'll need to give it fluids with a syringe and maybe make it's food liquid so you can also feed that through a syringe. A mix of wet catfood, a little bread and eggfood with water seems very effective.
Give it lots of bedding and rest, don't check on it more than you need to, any stress will cause it to die more quickly. So when you use the syringe, don't force it on the mouse, but put it gently in it's mouth without holding the mouse or taking it out of it's cage if possible.

I hope this is of help for you

About the biting, I've heard it happen before, it might be that they are fed up with being handled and they are trying to tell you off. Try handling them differently. (This is just a theory...)