First let's define what I'm talking about here. When a hamster is aggressive or otherwise 'attacks' only while in their cage or especially in their cage then they are described as "cage aggressive". This stems from what is usually termed as "cage territorialism". The hamster is territorial over their home and so resorts to aggression to defend their space. Cage aggression is sometimes also called "cage rage". Most of these hamsters are quite fine with being handled outside of their cage however. It seems to be most common among Russian Campbell dwarf hamsters, though any species of hamster can fall to this behaviour. It is especially evident when the hamster is kept in an undersized cage. Usually once their cage is upgraded to an adequate size they fall away from this behaviour. Other times it becomes habit and even with a large enough cage they are still cage aggressive.
This behaviour was not spoken about much when I first started keeping hamsters. Since it was a common behaviour in RC dwarfs they were often simply termed as 'evil' instead of trying to figure out why they were 'evil'. I became aware of it when I (and I tell this story a lot) had a RC dwarf in a 10 gallon tank, his name was Dusk. I thought he was evil as he always viciously attacked me when I tried to pick him up from his cage. I never thought to try handling him outside of his cage I assumed his behaviour would be the same. Several months later I finally got a 20 gallon long tank for Dusk. Within an hour of moving in, he let me pick him up and he never bit me again.
I began to pick up on this same behaviour in other people's hamsters. It started to become clear to myself as well as to many others that we weren't dealing with evil hamsters but a negative behaviour often picked up by hamsters as a result of undersized cages.
So for those people that believe that they have a cage aggressive hamster consider these next few points:
- How big is your cage? If it is too small (I recommend a bare minimum of 360 square inches of floorspace) than perhaps this is the driving force for your hamsters behaviour. This is just one reason to upgrade.
- Is your hamster ok with being handled outside of his or her cage? If not than perhaps your hamster just isn't socialized. If this seems to be the case then go here: Taming. Or it could be a combination of both too.
- Have you upgraded your hamster's cage and this behaviour is still persisting? Sometimes this is the case, it has become ingrained in your hamster as a habit and may never be broken. If this is the case then respect for their space on your part is required. This does not mean that they cannot be handled, but rather that they should only be handled where they are comfortable. That is, outside of their cage. Use a tube, a ladle, a cup or something for them to climb into from their cage and then once they are out of their cage try handling them. Most people seem to have no problem with this, it takes only a few seconds longer and you are respecting their space. Some people do this even if their hamster is not territorial.
The other issue with having a cage territorial hamster is that they (provided they are a dwarf species) often have issues with any cage mates. If you have multiple hamsters it is very important that you have a large enough cage for them. Otherwise you are going to end up needing two cages anyways because fights will ensue. It doesn't always happen right away, but very few pairs or groups can thrive in a small set up without issues arising eventually. In the end even if they don't fight, they don't seem to be very happy either, it's surviving not thriving.