what is that?

by Lily
(Seattle)

There is something white and bumpy on my Russian tortoise's butt, what is it?

I'm afraid I can't take him out of his habitat very much because the weather here is very cold. he spends most of his time sitting in one corner area of his habitat, which is approx 40" x 30". I use a mixture of play sand and coconut fiber as a substrate.
I feed him green leaf lettuce and Romain, sometimes small red yellow, and orange peppers, and sometimes pear cactus and dandelions. Also he gets pellets and calcium dust.
He is eating and pooing fine. I'm just concerned about the white bumps and wondering if it's normal/healthy to be in a small space so much. In the summer I will be able to take him outside, but not for a couple more months. Is there anything I could be doing different or better for Calvin?
Any suggestions, or insights greatly appreciated!
Thanks.