[Royal]

Pictures do these caves no justice. If you have never been to Carlsbad Caverns, you need to put this on your list of things to do. It is not the deepest or the biggest cave in the world, but it is the most beautiful. The Natural Entrance and the Big room are both self guided tours, in other words you are on your own. If you go during the off season in the winter and on a week day, you may find you have the cave(s) pretty much all to yourself. There is always a park ranger or two in the caves for your safety, and there are emergency phones should anyone need to call for help. Carlsbad National Park is open year round and is only closed on Christmas day.
If you have the time, stay until dusk so that you can witness the flight of the bats. At sunset about a 1/2 million Mexican freetail bats exit the cave for their nightly feeding.

During your descent in to the Natural Entrance, you will see bat cave, this is an area of the cave that the bats live. But you will not see a single one while you are in the cave, and the caves close before they exit.
No they will not bite, but it might not be a bad idea to wear a cap, with that many bats flying directly over your head, there is bound to be an accident or two.