There is a frog/toad in my basement?

There has been a frog or toad ( I think ) in my basement for at least a couple of months now. My family and I have no idea how it got in and how it's still alive. We don't know what it's been living off of. We have found no excrement anywhere, nor any other signs of a frog or toad. However, we frequently hear it croaking in the basement. Does anyone have any ideas as to what it may be and how/why it's been in my basement for so long?