Spider Bite, Black Widow

Spider Bite, Black Widow is a topic covered in the 5-Minute Emergency Consult.

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  • Syndromes caused by envenomation by black widow spider bite
  • Mechanism of toxicity:
    • Females are responsible for human envenomations
    • Venom contains potent neurotoxin, α-latrotoxin:
      • Causes cation-channel opening presynaptically, resulting in increased neurotransmitter release into synapses and neuromuscular junctions
      • Increased neurotransmitter release causes increased neurologic, motor, and autonomic effects
  • Morbidity and mortality are dose dependent
  • Severity of envenomation depends on:
    • Premorbid health of victim:
      • HTN or cardiovascular disease increase risk
    • Size and age of victim:
      • Children (i.e., smaller size for a given dose of venom) are at greater risk of morbidity and mortality.
    • Number of bites
    • Location of bite wounds
    • Size and condition of spider
  • Rarely fatal


Black widow spider features:
  • Appearance:
    • Glossy black with red markings shaped like an hourglass or a pair of spots on the ventral aspect of the globular abdomen
    • Females have 25–50 mm leg spans and 15 mm long bodies
  • Found throughout North America, except the far north and Alaska
  • Prefer dark sheltered hideaways such as garages, barns, outhouses, woodpiles, and low-lying foliage
  • Most bites occur during the warmer months when spiders are defending their webs and egg clutches

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