User blog comment:Le Rottweiler/Why is there a teleporter in Shub’s pit?/@comment-1496755-20150723141518

My personal hypothesis is that Shubby feeds off slipgate energy (if there is such a thing). The spiked sphere is the destination of a slipgate, and is thus saturated with these energies. So when it passes through her body, it charges her.

Why the sphere moves around - it could be a symbiote of some sort that allows Shub to see places where she can't go (due to being a large blob with tentacles), and it was conveniently designated to be the slipgate destination as well (to increase the slipgate energy feed).

At least that's the most meaningful thing I could come up with :P

I can also assume that Shubby probably did not believe that anyone would be able to access her lair... and even if someone did, that he would not be able to survive for long, in order to utilize the sphere for a telefrag.