The word "enemy" usually has a negative connotation with it, referring to something described as an "enemy" as something or somebody you don't like and usually have bad relations with, which an enemy can also be described as having negative intentions and being hostile. Therefore, the father probably dislikes the snake for multiple reasons, as snakes are known to be dangerous, and the father acknowledges it.
Also, depending on previous paragraphs, you may be able to conclude more and much clearer insight on the father's views and why he dislikes the snake and why he sees it as his "enemy".
