ill-treat vs prey on

ill-treat

verb
  • To treat someone or something badly or unkindly; to abuse or mistreat. 

prey on

verb
  • To exploit or victimize. 

  • To eat (as prey). 

  • To weigh heavily upon (a person's mind). 

How often have the words ill-treat and prey on occurred in a corpus of books? (source: Google Ngram Viewer )