From the EM Model
6.0 Environmental Disorders
6.1 Bites and Envenomations

Among the nearly 40,000 spider species and more than 100,000 species of insects, very few species are responsible for any morbidity and mortality in humans. Anaphylaxis is the most common reason for morbidity and mortality from Hymenoptera (wasps, bees, and ants) envenomation; it is estimated to occur in between 0.4% and 5% of the general population, with approximately 40 to 100 Americans dying because of it yearly, although these figures probably grossly underestimate the true numbers.¹ Emergency physicians should be able to recognize, evaluate, and manage spider and insect envenomations.

Case Presentation

A 45-year-old man presents complaining of chest pain and difficulty breathing; he had been mowing his lawn. His vital signs are blood pressure 85/42, pulse rate 52, respiratory rate 24, temperature 37.7° C (99.9° F), and oxygen saturation 88% on room air. Physical examination reveals an obese man who appears pale and is diaphoretic. He has dry mucous membranes. An S1 and S2 are noted, and pulmonary auscultation reveals expiratory wheezing bilaterally. Bowel sounds are diminished, and his abdomen is nontender. A diffuse urticarial rash is noted on his chest, back, arms, and legs. On further questioning, he says that a bee stung him while he was mowing.

Arthropod Envenomations

Widow

Five species of widow spiders are found in North America, Latrodectus bishopi, Latrodectus geometricus, Latrodectus hesperus, Latrodectus variolus, and Latrodectus mactans, with L. mactans being the most common. They are distributed across the continental United States and range into the southern Canadian provinces.² Many species are a shiny black with red markings, although both the color and markings can vary. The female spider is primarily responsible for clinically significant envenomations because the male’s fangs are not large enough to penetrate human skin. Widow spiders are generally not aggressive and only bite defensively.³