To the entomologist all insects have six legs; the layman tends to use the term "insect" to include the eight-legged spiders and mites. All these creatures are correctly classified as arthropods. Many thousands of the hundreds of thousands of recognised species of arthropods are found in the human environment-domestic, occupational and rec reational. Those species which are obligate parasites of man, the human scabies mite and the head and body lice, produce familiar clinical syndromes. They remain important in medical practice and have been the subject of a great deal of recent research....