earl vs marquis

earl

noun
  • Any of various nymphalid butterflies of the genus Tanaecia. Other butterflies in this genus are called counts and viscounts. 

  • A British or Irish nobleman next in rank above a viscount and below a marquess; equivalent to a European count. A female using the style is termed a countess. 

marquis

noun
  • Any of various nymphalid butterflies of the Asian genus Bassarona (or Euthalia). 

  • A nobleman in England, France, and Germany, of a rank next below that of duke, but above a count. Originally, the marquis was an officer whose duty was to guard the marches or frontiers of the kingdom. The office has ceased, and the name is now a mere title conferred by letters patent or letters close. 

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