Today, in the afternoon, I decided to clean up the right part of a terrarium in which I keep two tarantulas. The right part, since the terrarium is split into two sections, each housing one tarantula.
The tarantula, probably a Cyclosternum fasciatum, was hiding in a small hole it had dug under a stone. It had covered the bottom with silk, and next to it was a cast-off skin (exuvia).
In the above photo, the tarantula decided to leave its now exposed burrow. Notice the nice blue sheen on the upper part of the legs. In "top" part of the burrow you can see the cast-off skin, pushed to the side of the burrow by the tarantula.
I cleaned the stones a bit, and the substrate in the terrarium and restored the stones and pieces of wood back into place. The burrow of the tarantula was under the large stone in the left of the picture (back).