The animals which are harmful to man include a wide range. The predatory mammals which choose man as an article of diet are referred to mainly in writings on adventure. As one descends to the Reptilia, however, one finds much written on the venoms of snakes and other members of this group. Still farther down the scale come the Arthropoda, including, besides the spiders, scorpions, ticks and other arachnids, the immense and fascinating array of insects about which countless volumes have been contributed to scientific libraries. As one proceeds downward through the predatory worms, one comes to the lowest of all, the Protozoa, important agents of harm, either through their own activity or by collaboration with insects or higher animals.
The present consideration will be confined entirely to the class Hexapoda, or insects, which includes, according to various entomologists, thirty or more orders. Of these I need mention only a