While talking to the lady that i got my guineas from, she mentioned that they will indeed kill snakes, but she said the only ones that she has seen them kill are the rattlers that are able to buzz, she said that she seen a gopher snake (non toxic, no rattle) and the guineas didnt even bother with it. She also said the baby rattlers with no rattles arnt attacked by the guineas either.
She did go into detail on how the guineas kill the rattle snakes, and it is pretty amazing, not to mention how much they impact the tick population as well!!! I am still waiting to see how noisy they are, since mine are still keats!!!