inchworm vs spanworm

inchworm

noun
  • The larva of a moth of the family Geometridae. 

verb
  • To move in a looping fashion, like an inchworm. 

  • To crawl or creep slowly. 

spanworm

noun
  • A measuring worm or inchworm (Lepidoptera, Geometridae) 

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