crab louse vs louse

crab louse

noun
  • A parasitic insect, Pthirus pubis, that lives amongst the pubic hairs of humans and feeds on blood. 

louse

noun
  • A small parasitic wingless insect of the order Psocodea. 

verb
  • To remove lice from; to delouse. 

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