I've heard many times that the butter and the lesser started from 2 different wild caught snakes . They may have been different variations of the same line but they were found at different times so have bred different lines in the captive bred world. However since then, the lines have crossed so many times they may be indistinguishable. I like to think of them as different because I have multiple butter/lessers and my butter is much more of a bright yellow and my lessers are a pale yellow. The brown markings vary but in all the pictures I've seen, I still see more bright yellow in butter and pale in lesser. Something I have heard but not proven is that butters supposedly get brighter or retain more color with age where as lessers fade. In the end, it's relative. I believe they are different but have crossed a lot. Many argue they are the same. Believe what you would like