Hi. Definitely a Red knee. That bare looking bum is a result of him/her kicking off the urticating hairs on its abdomen. It's completely normal, and that bald spot will disappear with the next molt. It might reappear tho if it gets irritated and starts kicking those hairs at you again. Beware the hairs, especially when it gets bigger. They may make you itch like crazy, and do anything you can to avoid getting them in your eyes. It will definitely be a bad day.http://homepage.ntlworld.com/the.tarantula.store/common-questions.htm check that link out to learn more about them.