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My 16 yo female is showing nesting behavior. I placed her in a large cardboard box with access to water and soil however she chooses to dig in the cardboard instead. What should I do about this?

Nesting boxes often don't work, but the moment she it wanting to go is the time to put her in. They often have a preference as to when, so you might be able to figure it out. Ideally, she will want to go outdoors, but it might be too cold where you are.

It is too cold to allow her outside and she wants to dig a nest but she’s choosing cardboard over soil

Not sure how that will work out, but hopefully she'll keep trying. Most RES who cannot find a suitable area will eventually expel the eggs into the tank.