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For further information, see CMDT Part 38-56: Spider Bites & Scorpion Stings

Clinical Findings

  • Envenomation from most species of spiders in the United States causes only

    • Local pain

    • Redness, swelling

  • Venomous black widow spiders (Latrodectus mactans) cause

    • Generalized muscular pains

    • Muscle spasms

    • Rigidity

  • Brown recluse spider (Loxosceles reclusa) causes

    • Progressive local necrosis

    • Hemolytic reactions (rare)

  • Stings by most scorpions in United States cause only local pain

  • Stings by the more toxic Centruroides species (found in southwestern United States) may cause

    • Muscle cramps

    • Twitching and jerking

    • Hypertension, convulsions, and pulmonary edema (occasionally)


Black widow spider bites

  • Relieve pain with parenteral opioids or muscle relaxants (eg, methocarbamol, 15 mg/kg)

  • Calcium gluconate 10%, 0.1–0.2 mL/kg intravenously, may relieve muscle rigidity

  • Antivenom is available; because of concerns about acute hypersensitivity reactions, it is often reserved for very young or elderly patients and those who do not respond to the above measures

  • Horse serum sensitivity testing required (instruction and testing materials are in the antivenin kit)

Brown recluse spider bites

  • No universally accepted management

    • Some authorities recommend early excision of the bite site

    • Other experts recommend oral corticosteroids

  • Anecdotal reports claim success with dapsone and colchicine

Scorpion stings

  • No specific treatment other than analgesics is required for envenomations by most scorpions found in the United States

  • An FDA-approved specific antivenom is now available for Centruroides stings

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