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.