grub vs work one's butt off

grub

noun
  • An insect at an immature stage of its life cycle. 

  • Food. 

  • A dirty person. 

  • A despicable person; a lowlife. 

verb
  • To scavenge or in some way scrounge, typically for food. 

  • To dig; to dig up by the roots; to root out by digging; often followed by up. 

work one's butt off

How often have the words grub and work one's butt off occurred in a corpus of books? (source: Google Ngram Viewer )