Insecta

Members of the phylum ARTHROPODA composed or organisms characterized by division into three parts: head, thorax, and abdomen. They are the dominant group of animals on earth with several hundred thousand different kinds. Three orders, HEMIPTERA; DIPTERA; and SIPHONAPTERA; are of medical interest in that they cause disease in humans and animals. (From Borror et al., An Introduction to the Study of Insects, 4th ed, p1).