In much of the world, arthropod bites commonly serve as vectors that transport diseases such as malaria, leishmaniasis, West Nile virus, filariasis, and rickettsial diseases. In modern industrial societies, most bites are more of a nuisance than a potential carrier of a life-threatening illness.

Insects such as mosquitoes, fleas, and flies have six legs. Arachnids such as spiders have eight legs, a group that also includes ticks, mites, and scorpions. In the United States, mosquitoes, fleas, biting flies as well as ticks, spiders, bed bugs, chiggers, and lice account for the majority of bites. Mosquito and fly bites occur most often from outdoor exposures, particularly in the summer months. Flea bites are most often acquired indoors, from pets. Stings are often caused by bees, wasps, hornets, and fire ants. In arid areas, including much of the Southwest and parts of California, flying insects are less common, and crawling arthropods are the primary cause of bites and stings.

There is individual variability in the human attraction of insects, possibly related to pheromones. Furthermore, the reactions to bites and stings are probably related to individual hypersensitivity. Lesions occur as a result of the body's immune response to injected foreign chemicals and proteins introduced by a bite or sting.

Discussed in this chapter are waterborne stings and seashore infestations that occur from visiting the beach and swimming in salt or freshwater which exposes people to a variety of organisms. Such encounters can result in seabather's eruption and cutaneous larva migrans. Encounters with jellyfish (e.g., sea nettle, Portuguese man-of-war, thimble jellyfish) can also cause skin reactions.