Where does the phrase “snake in the grass” originate and What does snake in the grass mean?

We owe the proverbial saying “snake in the grass” to the Roman poet Vergil (70-19 B.c.).

In the third Eclogue is the line Latet anguis in herba, “A snake lurks in the grass.”

Apperson reports the appearance of this Latin proverb also in a political song in England round the year 1290: Cum totum fecisse putas, latet anguis in herba, “Though all appears clean, a snake lurks in the grass.”

The saying was used frequently thereafter.

The earliest English translation was Edward Hall’s Chronicles (1548): The Union of the Two Noble and Illustre Famelies of Lancestre and Yorke: “But the serpent lurked vnder the grasse, and vnder sugered speache was hide pestiferous poyson.”

The French put the snake under a rock, quelque anguille sous roche.