Black Widow Spider

Aka: Black Widow Spider, Latrodectus mactans, Widow Spider, Latrodectism, Widow Spider Bite, Poisoning due to Black Widow Spider Venom, Black Widow Spider Venom

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II. Epidemiology

  1. Most commonly active in warmer months
  2. Occurs throughout the United States except for Alaska

III. Types: Widow Spider scientific names

  1. More than 30 species worldwide
  2. Most common in United States
    1. Latrodectus mactans (Southern Black Widow)
      1. South Eastern U.S.
    2. Latrodectus hesperus (Western Black Widow)
      1. South Western U.S. (Arizona, New Mexico, Texas, Oklahoma, Kansas, Nevada, Utah, Southern California)
      2. Also found in Mexico
    3. Latrodectus variolus (Northern Black Widow)
      1. Northern U.S. (New England states) and southeastern canada
  3. Less common in United States
    1. Latrodectus bishopi
    2. Latrodectus geometricus (Introduced brown Widow Spider)
      1. Southern United States
      2. Yellow-orange hour glass and milder venom

IV. Background: Lactrodectus mactans (Southeastern black widow)

  1. Female (only female delivers venomous bite)
    1. Glossy ink-black Spider
    2. Abdomen, large and globular
    3. Red hourglass on underside (ventral) Abdomen may be difficult to visualize
    4. More venomous than males
    5. Leg span : 3-4 cm (medium size Spider)
  2. Male
    1. Grey coloration
    2. Stripes or spots
    3. Rarely transmit significant venom with bite
    4. Leg span: 1.6 to 2.0 cm (Half the female size)
  3. Spiderlings
    1. Orange, brown and white striped pattern (zebra-like)
    2. Change color with molting
  4. Web
    1. Irregular, chaotic-patterned heavy, strong web
    2. Adult female Spider rarely leaves web
  5. Images
    1. ErSpiderBlackWidow.jpg

V. Background: Habitat

  1. Quiet, dark areas of structures (e.g. dark undisturbed corners) or rock crevices
  2. Indoors (Buildings)
    1. Dark garages
    2. Basements
    3. Stables
  3. Outdoors
    1. Yard debris
    2. Rock crevices
    3. Wood piles
    4. Overhangs
    5. Abandoned rodent holes

VI. Pathophysiology

  1. Highly venomous Neurotoxin: a-Latrotoxin
    1. Toxin binds irreversibly to presynaptic Neuron receptors
    2. Stimulates large presynaptic Acetylcholine release
  2. Bite results in systemic toxicity (Latrodectism)
    1. Muscle spasms and myalgias
    2. Excessive adrenergic stimulation
    3. Excessive Cholinergic stimulation

VII. Symptoms

  1. Initial
    1. Bite felt as pinprick with minimal initial pain
  2. First 10 to 20 minutes
    1. Significant pain and throbbing develops at bite site
    2. Most bites are limited to local reaction (without Latrodectism)
  3. Next 2 to 3 hours: Latrodectism (Systemic Reaction with Acetylcholine Release)
    1. Symptoms start at the region of the bite and progress proximally
    2. Symptoms recurr in waves for up to 48 to 72 hours
    3. Constitutional (more severe cases)
      1. Generalized sweating
    4. Musculoskeletal symptoms
      1. Diffuse, progressive myalgias in 100% of patients
    5. Cardiopulmonary symptoms (associated with upper extremity bites)
      1. Crampy Chest Pain or chest tightness
      2. Dyspnea
    6. Gastrointestinal Symptoms (associated with lower extremity bites)
      1. Abdominal cramping (64%)
      2. Board-like rigidity (may be confused with peritonitis)
      3. Nausea and Vomiting (36%)
    7. Facial Symptoms
      1. Flushed sweating face
      2. Contorted, Painful grimace
      3. Conjunctivitis
      4. Trismus of masseter Muscles
      5. Blepharitis
      6. Facial Edema
    8. Neurologic Symptoms
      1. Headache (27%)
      2. Anxiety
      3. Restlessness
      4. Paresthesias
      5. Seizures
      6. Weakness
      7. Tremors

VIII. Signs

  1. Bite wound
    1. Two small central red fang marks on blanched skin
    2. Surrounded by erythematous rings (target appearance)
    3. Bite may also appear as wheal and flare pattern
    4. Localized diaphoresis
    5. Muscle Fasciculations in the involved extremity
  2. Systemic (more severe cases)
    1. Fever
    2. Hypertension
    3. Diaphoresis
    4. Tachycardia
    5. Shock
    6. Abdominal Pain (with rigid Abdomen)
    7. Back pain

IX. Grading

  1. Grade 1
    1. Asymptomatic other than localized pain at Envenomation site
    2. Normal Vital Signs
  2. Grade 2
    1. Muscle pain in extremity with Envenomation
    2. Pain radiation into chest (arm bites) or Abdomen (leg bites)
    3. Local extremity diaphoresis
    4. Normal Vital Signs
  3. Grade 3
    1. Generalized Muscle pain in back, Abdomen and chest
    2. Generalized diaphoresis
    3. Abnormal Vital Signs (e.g. Hypertension, Tachycardia)
    4. Headache
    5. Nausea and Vomiting
  4. References
    1. Clark (1992) Ann Emerg Med 21(7): 782-7 [PubMed]

X. Differential Diagnosis

  1. Toxin Ingestion
  2. Angina
  3. Pneumonia
  4. Asthma
  5. Acute Abdomen (Peritonitis)
  6. Nephrolithiasis

XI. Course

  1. Symptoms resolve over 2-3 days
  2. Mortality approaches 1%
  3. Shock or death are more common in children and elderly

XII. Labs: Used to differentiate from other conditions

  1. Complete Blood Count
    1. Distinguish from peritonitis
  2. Urinalysis
    1. Distinguish from Urinary Tract Infection
  3. Serum Creatine Phosphokinase or Lactate Dehydrogenase
    1. Distinguish from Rhabdomyolysis

XIII. Management: General

  1. General
    1. Cold compresses or ice pack (prevents toxin spread)
    2. Thorough Wound Cleansing with soap and water
    3. Corticosteroid ointment
    4. Tetanus Prophylaxis as needed
    5. Oral Analgesics (NSAIDs, Acetaminophen)
  2. Muscle spasms, rigidity, pain
    1. Consider in Grade 2 (oral agents) and Grade 3 (Parenteral agents) reactions
    2. First-line therapy: Benzodiazepines
      1. Diazepam (Valium)
        1. Infants/Toddlers: 0.2-5 mg slow IV bolus
        2. Older children and Adults: 10 mg slow IV bolus
    3. Older regimens that have fallen out of favor
      1. Magnesium infusion
        1. Not effective in studies
      2. Calcium Gluconate
        1. Not effective in studies
        2. Adult dose: 10 ml of 10% solution) slow IV infuse
        3. Can be repeated every 4 hours
      3. Methocarbamol (Robaxin)
        1. Adult dose: 10-30 ml slow IV infuse
        2. Calcium is more effective
  3. Opioid Analgesics
    1. Consider in Grade 2 (oral agents) and Grade 3 (Parenteral agents) reactions
    2. Monitor for respiratory depression (especially in younger patients)
  4. Severe Hypertension
    1. See Intravenous Antihypertensive
  5. Disposition
    1. Observe for 6 hours
    2. May discharge home if no concerning symptoms or signs
    3. Consider hospital observation for Grade 3 reactions, children, and those with cardiovascular disease

XIV. Management: Antivenin (horse serum)

  1. Indications (rarely indicated, <4% of confirmed cases)
    1. Critical Envenomation (Grade 3 bites)
    2. Respiratory arrest
    3. Seizures
    4. Hypertensive heart disease
    5. Young Children or elderly
    6. Pregnant women
  2. Dosing
    1. Skin test first before dosing
      1. Evaluate for sensitivity to horse serum (5% risk of reaction)
    2. IV: 2.5 ml (1 vial) in 100 to 250 ml NS IV over 2 hours
  3. Adverse effects: Serum Sickness
    1. Risk may be greater than risk of death by Spider Bite
  4. Efficacy
    1. Relieves symptoms within 1-2 hours
    2. Efficacious up to 90 hours after bite

XV. Complications

  1. Life threatening reactions are rare
  2. Pulmonary Edema
  3. Cardiomyopathy
  4. Rhabdomyolysis
  5. Acute Kidney Injury
  6. Cardiovascular Collapse

XVI. Precautions

  1. Hospitalize severe cases or significant comorbidity
  2. Cohorts to consider hospitalization
    1. Pregnancy
    2. Extremes of age (very young or old)
    3. Coronary Artery Disease
    4. Severe Hypertension

XVII. References

  1. Cowling and Ferreri (2019) Crit Dec Emerg Med 33(2): 17-25
  2. Cowling and Lowes (2024) Crit Dec Emerg Med 38(1): 4-13
  3. Diaz (2007) Am Fam Physician 75(6):869-73 [PubMed]
  4. Herness (2022) Am Fam Physician 106(2): 137-47 [PubMed]
  5. Ibister (2011) Lancet 378(9808): 2039-47 [PubMed]
  6. Juckett (2013) Am Fam Physician 88(12): 841-7 [PubMed]
  7. Koh (1998) Postgrad Med 103(4): 235-50 [PubMed]

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