Spider bites

Revision as of 23:58, 4 November 2013 by Ostermayer (talk | contribs) (Black Widow)

Brown Recluse


  • White "violin" shape

Clinical Features

  1. Bite is initially painless
  2. Mild reaction
    1. Most common
    2. Mild erythematous lesion that later becomes firm and heals without scar
  3. Severe reaction
    1. Begins w/ mild-severe pain several hrs after bite accompanied by erythema and swelling
    2. Hemorrhagic blister then forms surrounded by vasoconstriction-induced blanched skin
    3. By day 3 or 4 hemorrhagic area may become ecchymotic
      1. Leads to "red, white, and blue" sign (erythema, blanching, ecchymosis)
    4. By end of first week ecchymotic area may become necrotic w/ eschar formation
  4. Systemic effects
    1. Rare
    2. Occur predominantly in children 24-72hr after the bite
      1. Include nausea/vomiting, fever, arthralgias, thrombocytopenia, rhabdo, renal failure


  1. Local wound care
  2. Abx are indicated only if signs of infection exist; secondary infections are uncommon

Black Widow


  • Red hourglass on otherwise black spider


Envenomation causes release of acetylcholine and norepinephrine from the nerve terminals causing muscle cramps, tachycardia and hypertension

Clinical Features

  1. Local
    1. Pinprick sensation; then increasing local pain that may spread to entire extremity
    2. Erythema appears 20-60 min after the bite
    3. Pain begins to abate after several hours and disappears by 2-3d
  2. Systemic
    1. Muscle cramp-like spasms in large muscle groups (although exam rarely reveals rigidity)
    2. Pain becomes generalized
      1. Severe abdominal wall musculature pain and cramping
    3. HA, n/v, diaphoresis, photophobia, dyspnea
    4. A-fib, myocarditis, priapism, and death are rare


  1. Pain and muscle spasms
    1. Opiods and benzos
  2. Systemic illness
    1. Antivenin
      1. Consider for:
        1. Children
        2. Pregnant women
        3. Elderly


  1. Consider admission for:
    1. Symptoms of moderate envenomation
    2. Pregnant women
    3. Children
    4. Pts w/ preexisting cardiovascular disease or HTN


Clinical Features

  1. Abdominal hairs may be flicked a short distance when threatened
    1. Rarely penetrate human skin but can imbed deeply into conjunctiva and cornea
  2. Bites can be painful but systemic symptoms other than fever are unusual


  1. Red eye and pain after handling a tarantula necessitates an ocular exam
    1. Hairs may be difficult to detect on slit lamp
  2. Treatment is surgical removal of hairs and topical steroids

See Also

Bites and Stings


  • Tintinalli
  • Rosen's