Is anyone else as curious as me as to what that is about? we havent heard about it for many episodes also.
"Real is a matter of perception." Peter Bishop
Watch "Unleashed" again. I presume alt-Charlie was attacked by the same or a similar hybrid animal which included an arachnid (e.g., scorpion) in its makeup. Without Walter to come up with a cure, he's on a maintenance drug to keep them from growing.