Moonstone is right...adult females can [ but don't always] produce infertile eggs with no male in sight. You don't need to provide a messy nest box unless your girl starts scratching around the cage alot. Some dragons will scratch around at times anyway, but a gravid female will usually do so with much greater urgency. Another sign is a huge belly of course, and then loss of appetite suddenly. Healthy females have no problem laying, just be sure to feed well and provide proper UVB as well as calcium supplements.