Spider bites

Revision as of 15:50, 22 March 2019 by Wgalvin85 (talk | contribs) (I added general history, evaluation, and treatment of undifferentiated spider bites)


Differential Diagnosis

Envenomations, bites and stings


  • Determine circumstances of bite to assess consistency with spider habitat and behavior
    • Indoors vs outdoors
    • Day vs night
    • Geographic location (recent travel)
  • Appearance of the spider if seen
  • Dead spiders can be preserved in 70% EtOH and later identified by arachnologists or entomologist

Clinically important spider genera by geographic region

  • North America
    • Loxosceles
    • Latrodectus
    • Tegenaria
  • South America
    • Loxosceles
    • Latrodectus
    • Phoneutria
  • Africa
    • Loxosceles
    • Latrodectus
  • Europe
    • Loxosceles
    • Latrodectus
  • Australia
    • Atrax
    • Hadronyche
    • Latrodectus
  • Asia
    • Latrodectus

Physical Exam

  • No pathognomonic signs proving lesion is a spider bite
  • Assess both bite site and for systemic signs
  • Bite Site
    • Location
      • Spider bites more common when clothing is tight against skin
    • Number of bites
      • Multiple bites suggest parasitic insect and not spider
    • Appearance of bite
      • Erythema, pallor, hemorrhage, induration, tenderness, paresthesia, vesicles
  • Systemic findings
    • Abnormal vital signs
    • Altered mental status
    • Abdominal pain
    • Diaphoresis
    • Generalized rash
    • Muscle fasciculations, spasm, or tenderness


  • Clean area of bite
  • Tetanus prophylaxis
  • Analgesics
  • Hydration
  • Surgical follow up if indicated for debridement of necrotic area
  • Antivenom is indicated only for specific envenomation
  • No proven benefit for corticosteroids
  • No indication for antibiotics unless concern for cellulitis

See Also


  • Boyer LV, Binford GJ, Degan JA. Spider Bites. In Auerbach PS, Cushing TA, Harris NS. Auerbach’s Wilderness Medicine. 7th ed. Philadelphia, PA: Elsevier; 2017: 993-1016.