varmint vs vermin

varmint

noun
  • An obnoxious person or troublemaker. 

  • A pestering animal such as one that kills or harasses a farmer's livestock or crops. 

vermin

noun
  • Obnoxious, or mean and offensive person or people. 

  • Any one of various common types of small insects or animals which cause harm and annoyance. 

  • Animals that prey on game, such as foxes or weasels. 

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