estimated 899 species of tick in the world estimated 899 species of tick in the world Purdue Department of Medical Entomology estimated 899 species of tick in the world 90 tick species found in the U.S. estimated 899 species of tick in the world estimated 899 species of tick in the world Purdue University Medical Entomology: Ticks estimated 899 species of tick in the world 90 tick species found in the U.S.