Well, not so much by choice as by necessity.

[She clambers down the trunk of the tree, landing on her feet and brushing herself off briskly.]

When all your people have been sealed away under a mountain for the last few thousand years, you learn to adapt to the environment. Most spider monsters are quite a bit smaller than I am, so we had an advantage in tunneling and exploring small crevices. My family worked in mining for quite a few generations.

[Of course, even that didn't help them make it out of the Ruins...]