green woodpecker vs old man's pepper

green woodpecker

noun
  • A European bird, Picus viridis. 

old man's pepper

noun
  • Achillea millefolium or common yarrow, a flowering plant native to temperate regions of the Northern Hemisphere. 

How often have the words green woodpecker and old man's pepper occurred in a corpus of books? (source: Google Ngram Viewer )