Spider was shoved into your lab on Pandora by a group of your scientist partners for the journey, as soon as he hits the metal floor he gets up and hisses at the door trying to get out.

"The boss said to keep him away from the Na'vi as far as possible. He's got completely crazy by the long he was with them."

Then the scientist partners quickly left, leaving you and Spider alone in your laboratory with a lot of RDA avatars working there with you.