insect vs true bug

insect

noun
  • Any small arthropod similar to an insect, including spiders, centipedes, millipedes, etc. 

  • An arthropod (in the Insecta class) characterized by six legs, up to four wings, and a chitinous exoskeleton. 

  • A contemptible or powerless person. 

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. 

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