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Arthropoda means "joint-footed" in Latin and describes arthropods' jointed bodies and legs connected to a chitinous exoskelelton.2 The majority of arthropods are benign to humans and environmentally beneficial. Some clinicians regard bites and stings as inconsequential and more of a nuisance than a threat to life. However, some spiders have toxic venoms that can produce dangerous, painful lesions or significant systemic effects. Important clinical syndromes are produced by bites or stings from animals in the phylum Arthropoda, specifically the classes Arachnida (spiders, scorpions, and ticks) and Insecta (bees, wasps, hornets, and ants) (Table 119–1). Infectious diseases transmitted by arthropods, such as the various encephalitides, Rocky Mountain spotted fever, human anaplasmosis, babesiosis, and Lyme disease, are not discussed in this chapter.

Table 119–1. Insects and Other Arthropods That Bite, Sting, or Nettle Humans

Arthropoda comprises the largest phylum in the animal kingdom. At least 1.5 million species are identified, and half a million or more are yet to be classified. It includes more species than all other phyla combined (Fig. 119–1).2 Araneism or arachnidism results from the envenomation caused by a spider bite. "Bites" are different from "stings." Bites are defined as creating a wound using the oral pole with the intention for either catching or envenomating prey or blood feeding.84,185 "Stings" occur from a modified ovipositor at the aboral pole that is also able to function in egg laying as in bees and wasps. Stinging behavior typically is used for defense. Most spiders are venomous, and the venom weakens the prey, enabling the spider to secure, neutralize, and digest their prey. Spiders in general are not aggressive toward humans unless they are provoked. The chelicerae (mouthparts comprised of basal section and hinged fang) of many species are too short to penetrate human skin.

Figure 119–1.

Taxonomy of the phylum Arthropoda.

Spiders can be divided into categories based on whether they pursue their prey ...

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