bilberry vs bog bilberry

bilberry

noun
  • The shrub of the above-mentioned plant. 

  • Vaccinium myrtillus, the wild European blueberry of the cowberry family. 

bog bilberry

noun
  • A shrub native of the cool temperate areas of northern hemisphere, Vaccinium uliginosum, and the berry of that shrub. 

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