why does my dog chew on my other dogs collar?

when we leave the house we put both dogs in one big cage...no matter how long we are gone one of the dogs chews the other ones collar off!? why is she doing this?

Because you allow it too. A dog will chew on anything as long as you allow them to, and until you stop the dog, it will continue.

Maybe because you are not scolding them, or because she wants the other dog to "play" with her. If a dog wants attention from another dog in the house, (s)he will often try to nag them to try to get them to play with them. Next time you see this happening, scold the other dog, otherwise they will not stop doing it.

Usually they chew on another dog's collar during a struggle for dominance. In the wild, the mother will scruff her pups by the neck skin and pick them up. Sometimes it's to move them to a safer location. At other times, it's a means of correction. Dogs will do that to each other and shove and lead the one they've scruffed up to display dominance. I'd recommend either removing their collars before you leave the house, or separating them while you're gone.

A couple of things you might want to do is, take each of their collars off when you leave. Another, what about buying some toys? They may be getting bored.