green woodpecker vs milfoil

green woodpecker

noun
  • A European bird, Picus viridis. 

milfoil

noun
  • Any of several similar pungent Eurasian herbs, of the genus Achillea 

  • Common yarrow, Achillea millefolium. 

  • Any plants of the genus Myriophyllum; water milfoil. 

How often have the words green woodpecker and milfoil occurred in a corpus of books? (source: Google Ngram Viewer )