Difference between revisions of "Spider bites"

m (Rossdonaldson1 moved page Spider Bites to Spider bites)
(No difference)

Revision as of 14:20, 11 March 2015

Brown Recluse


  • Brown violin shape on cephalothorax (fiddleback)
  • In Southern midwestern US
  • Loxosceles family


  • Venom contains variety of cytotoxic enzymes causing necrotic wound

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, DIC, rhabdo, renal failure


  1. Local wound care
  2. Abx are indicated only if signs of infection exist; secondary infections are uncommon
  3. Although some texts recommend Dapsone, it has been shown to be of limited benefit and is associated with hemolysis in G6PD patients and als methemoglobinemia

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

Review Questions

Environmental emergencies question – Regarding black widow and brown recluse spider envenomations, which of the following is FALSE?

Black widow spiders (BWS) are found in the temperate regions of six continents and are widespread through North America, including the western United States (California included).
Signs and symptoms associated with BWS (e.g. diffuse pain, muscle cramps, tachycardia, and hypertension) usually develop begin within 30 to 120 minutes of the envenomation.
After antivenom for BWS is administered, symptoms typically resolve within 30 minutes, with complete relief within 2 hours.
Brown recluse spider (BRS) envenomation is most common in west coast states, such as California.
Most bites from BRS have a benign clinical course, but necrosis with induration and eschar formation may occur, and systemic effects, such as fever, chills, headache, malaise, arthralgia, and myalgias progress after more than 24 to 48 hours and resolve by 72 to 96 hours post bite.

See Also

Bites and Stings Envenomation


  • Tintinalli
  • Rosen's