What is the origin of the idiom "snake in the grass" and when to use it?

The origin of the idiom "snake in the grass" can be traced back to ancient times, rooted in the association of snakes with cunning and danger. The phrase has its origins in classical literature, such as Aesop's fables and Virgil's works, where snakes symbolized deceitfulness and hidden threats. Over time, the expression evolved to represent individuals who appear harmless or friendly on the surface but possess malicious intentions or act in a treacherous manner.