Feral Keidran are Keidran that have succumbed to their Feral Mode and have gone fully animalistic. The only known feral Keidran shown in the comic so far is a tiger Keidran that had dark hair and who Trace initially mistook for Flora. Upon seeing her front, he knew it was not Flora and she instantly attacked him. Relying only on instinct, she could only respond to a situation with a very basic understanding. When the real Flora came and Keith, the feral stayed for a few moments before fleeing into the woods, possibly thinking she was going to be attacked. Flora stated it was too late for her to be returned to normal.
Feral Keidran are animalistic and aggressive, but attempting to mate with the opposite sex at random is not a symptom of being feral, as Flora says that all Keidran females are like that when in heat, feral or not.