Over the past few years I have had over 20 American rat snakes. Four have been Texas Rat Snakes. None of my Texans have been biters. I think that this is all a myth. You get a young CB Black, Texas, Yellow, Everglades, or Gray, handle it often and gently, and you will have a nice adult. These snakes only differ in color.
Another myth, from what I can tell, is that of a pure breed leucistic Black Rat Snake. I have never seen a single report of anyone finding one in the wild, (They become lunch too quickly.) At this point in time, if you were to find one in the wild, (except maybe in very remote wilderness areas) you would have to consider the possibility that it was a pet that escaped since these snakes are now common in the trade. Since the subspecies of obsoleta (obsoletus) differ morphologically only in color, how could you tell one subspecies from another when they lack all the cells that produce skin color?
