Phalangium opilio vs harvestman

Phalangium opilio

harvestman

noun
  • A field-worker who works to gather in the harvest. 

  • An order of terrestrial, non-venomous arachnids with often very long legs: Opiliones. 

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