blue angel vs glaucus

blue angel

noun
  • A mollusc of genus Glaucus. 

  • A blue flame produced by lighting one's flatus. 

glaucus

noun
  • Any member of the genus Glaucus of nudibranchiate mollusks, found in the warmer latitudes, swimming in the open sea, strikingly colored with blue and silvery white. 

  • Citrus glauca, the desert lime, a thorny shrub species endemic to semi-arid regions of Australia. 

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