Widow Spider Bite (Latrodectism)


  • Latrodectus Mactans (black widow spider, show-button spider)
    • Seasonal Prevalence: most black widow bites occur between April-October in the United States
    • Geography: found in USA and Canada (black widow is most abundant in southeastern United States)
      • Spider resides in dark spaces wood piles, rock piles, sheds, garages, and basements
    • Female (which bites humans) is black with 1 cm body, 5 cm legspan, and has red hourglass mark on ventral abdomen
    • Spider is aggressive and bites on slight provocation (typically when trapped or web is disturbed)
  • Latrodectus Bishopi (red-legged widow spider)
    • Geography: found in Florida
  • Other Latrodectus species
    • Found in other temeperate and subtropical parts of the world


  • Alpha Latrotoxin (Neurotoxin) in Venom
    • Lack of local necrosis
    • Binds irreversibly to nerves and depletes acetylcholine and norepinephrine from presynaptic nerve terminals
    • Clinical Effects
      • Neuropathy -> acute hypoventilation
      • Autonomic activation
      • Diffuse central and peripheral nervous system excitation


  • CBC: leukocytosis

Clinical Manifestations

Widow Spider Bite Site

  • Asymptomatic bite site: occurs in many cases
  • Fang puncture sites at bite site: uncommon
  • Momentary sharp pain at bite site: however, this is often not prominent on exam

Neuro Manifestations

  • Anxiety
  • Painful Muscle Cramps/Spasms of Extremities and Trunk: cramping pain begins within 15-60 min after bite
  • Headache
  • Hyperreflexia (see Hyperreflexia)
  • Weakness
  • Twitching/Tremor/Fasciculations (see Tremor)
  • Parasthesias of Hands/Feet (see Peripheral Neuropathy)
  • Intracerebral Hemorrhage

Cardiac Manifestations

GI Manifestations

  • Abdominal Pain with Rigidity (see Abdominal Pain): due to muscle spasms
    • However, characteristically, abdomen is not tender on exam
  • Nausea/Vomiting (see Nausea and Vomiting)

Pulmonary Manifestations

  • Labored Respirations: due to respiratory muscle weakness
  • Acute Hypoventilation/Respiratory Failure (see Acute Hypoventilation)

Renal Manifestations

Other Manifestations

  • Salivation
  • Diaphoresis/Sweating
  • Fever (see Fever)
  • Uterine Contractions/Pre-Term Labor


Treatment of Pain at Bite Site

  • Spontaneous Resolution: pain at bite site usualy subsides within several hours (although recurrence over the next 2-3 days are common)
  • Analgesics: may be required
  • Hot Bath: prompt, but temporary relief of pain
  • RICE Therapy
    • Rest
    • Ice
    • Compression
    • Elevation

Treatment of Muscle Spasms

  • Spontaneous Resolution: painful spasms begin to subside within the first 12 hrs (but may recur for days-weeksbefore fully resolving)
  • Calcium Gluconate
    • Administration: (10%-10 mL IV over 10-20 min)
    • Clinical Efficacy: transient cessation of muscle cramps
  • Benzodiazepines: useful for muscle spasms
  • Methocarbamol (Robaxin) (see Methocarbamol)
    • Administration: IV
    • Clinical Efficacy: may relieve muscle spasms

Widow Spider Antivenom

  • Administration: 1 vial in 50 mL of NS IV given over 15 min
    • May need to test for hypersensitivity before use
    • Effective with a few hrs -> may repeat PRN
  • Clinical Efficacy
    • Controversial: indicated mainly for uncontrolled hypertension, pregnancy, eizures, or respiratory arrest
  • Side Effects

Tetanus Prophylaxis

  • Indicated


  • Deaths: have been reported (mostly in children, elderly, and debilitated)


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