Widow Spider Envenomation Treatment & Management

Updated: May 28, 2020
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Prehospital Care

Support the airway, breathing, and circulation per advanced cardiac life support (ACLS) protocols with oxygen, monitors, and intravenous fluid resuscitation.

Negative-pressure venom extraction devices (eg, the Extractor, Sawyer Products) have not been evaluated for treatment of widow spider envenomation.

Electric shock and various folk and herbal remedies lack therapeutic value and are potentially harmful.

Do not give antivenom in the field because of the risk of severe allergic complications. [17]

Attempts to secure the spider may be helpful in confirming widow spider envenomation as long as it can be done safely and does not delay transport.

Because these envenomations are exceptionally painful, analgesia is essential. Intravenous opioids are preferred initially.


Emergency Department Care

Supportive care is the mainstay of treatment. Ensure a patent airway and adequate oxygenation and ventilation. Maintain euvolemia. Symptomatic treatment of pain and muscle cramping can be accomplished with opioids and benzodiazepines.

Hypertension is common but usually resolves once the pain and muscle cramping are relieved. Intravenous antihypertensives such as nitroprusside, nicardipine, or labetalol are recommended for patients with conditions in which hypertension must be avoided (eg, coronary artery disease).

Envenomation severity can be classified as outlined below.

Grade 1—Mild—is characterized by the following:

  • Local pain at envenomation site

  • Normal vital signs

Grade 2—Moderate— is characterized by the following:

  • Muscular pain in the envenomated extremity

  • Extension of muscular pain to the abdomen if bitten on a lower extremity or to the chest if envenomated on an upper extremity

  • Local diaphoresis of envenomation site or involved extremity

  • Normal vital signs

Grade 3—Severe—is characterized by the following:

  • Generalized muscular pain in the back, abdomen, and chest

  • Diaphoresis remote from envenomation site

  • Abnormal vital signs (blood pressure >140/90 mm Hg, pulse >100)

  • Nausea and vomiting

  • Headache

Antivenom should be given for pain unresponsive to opioid analgesia and/or imminent risk of severe complication of envenomation (see Treatment/Complications). The risk of allergy to antivenom must be weighed against the benefit of relieving prolonged discomfort, avoiding hospitalization, and preventing complications. [17]


Medical Care

Admission to the hospital is generally indicated for the following patients, subject to clinical judgment:

  • Severely symptomatic children [8]
  • Pregnant women
  • Patients with a history of hypertension or heart disease
  • Patients with intractable pain and contraindications to antivenom
  • Patients with unusual complications of envenomation
  • Patients who develop anaphylaxis to antivenom

Discharge patients who experience relief with opioid analgesics, sedative-hypnotics, and/or antivenom (after a period of observation).

Antivenom administration may reduce the need for hospitalization.



Local poison control centers may assist management of difficult envenomations.

The Antivenom Index, published by the American Zoo and Aquarium Association and the American Association of Poison Control Centers, lists the locations, amounts, and various types of antivenom stores.



Antivenom-associated complications

Anaphylaxis, a type I (immediate) hypersensitivity reaction that may be life threatening, is characterized by urticaria, wheezing, and shock. Physician/provider fear of anaphylaxis often precludes appropriate antivenom treatment for widow spider envenoming; however, estimates of adverse reactions suggest a rate of only 3.5%. [18] Nevertheless, some dramatic cases are reported. Risk factors may include previous exposure to horse serum or antivenom or a history of reactive airways. It is treated with epinephrine, antihistamines, steroids, and ventilatory/circulatory support. Two deaths have been reported from anaphylaxis to widow spider antivenom in the United States. One case involved the death of an asthmatic patient after undiluted antivenom was given as an intravenous bolus. The patient developed bronchospasm refractory to medical therapy. [19] The second case also involved an asthmatic patient, but the anaphylaxis occurred during an appropriately diluted antivenom infusion. A subcutaneous test dose had been given prior to the infusion, and no reaction was found. Several minutes into the infusion, the patient developed anaphylaxis and cardiac arrest, required a prolonged resuscitation, and eventually died. [20]

Serum sickness, a type III (delayed) hypersensitivity reaction characterized by fever, urticaria, lymphadenopathy, and arthritis, may occur 5 days to 3 weeks after antivenom administration. It usually is benign, self-limited, and treated with antihistamines and steroids. Serum sickness is dose-related and uncommon following administration of widow spider antivenom because of the small amounts (1-2 vials) needed.

Also see Presentation/Complications.



Pesticides may prevent exposures to widow spiders at home.

Eliminate spider food and habitat.

Shake sheets, shoes, and clothing before donning, which may shake out a spider.

Keep beds away from walls, which may prevent spiders from crawling into bed.

Brush, do not crush. If a spider is seen on the body or clothing, it should be brushed off rather than crushed. Crushing the spider is more likely to elicit a bite response.

Use plastic bags with slide-lock closure (eg, Ziploc) for garage-stored clothes rather than twist-tie closure mechanism.

Do not leave children’s toys outside.





Long-Term Monitoring

Instruct patients to return if any of the following symptoms occur:

  • Hematuria
  • Rash
  • Joint pain
  • Swollen lymph nodes
  • Difficulty breathing
  • Signs of infection

Advise patients that if treated symptomatically with pain medications and benzodiazepines, pain may come and go for up to days to weeks after envenomation.

If patients have been treated with antivenom, discuss signs of serum sickness (as noted above) and warn them of its possible occurrence in 3-21 days.