true bug vs vermin

true bug

noun
  • Any of various insects of the order Hemiptera and in particular of the suborder Heteroptera, that are wingless or have two pairs of wings, and have mouthparts adapted for piercing and sucking. 

vermin

noun
  • 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. 

  • Obnoxious, or mean and offensive person or people. 

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