Here's an S. castaneiceps gigantea (just made that name up in case noobs are looking). I put it with a pede I know is a female last night. I really think this big one is a female, that's why I tried it. The smaller one just turned around and they sparred a little with the terms but that was it. So, more evidence it's a female if you ask me. I don't want to try to mate it with a male right now, hoping she already has. That cactus is 16 1/2 inches high.