Insects and related animals such as spiders attack human beings in several related ways. These may be classified as carriers of disease, such as deer ticks that carry Lyme disease, irritated attackers, such as bees and wasps that sting in defense of nests or in counterattack, and offensive attackers, such as mosquitos. Although we will consider all these classes, the concentration will be on the last type, since these have traditionally been most likely to ruin vacations and country living. Among the latter are most prominently mosquitos, horse flies, gnats, midges, and black flies.