Black Widow Spider Bite

Most people avoid spiders. Many fear them. Scary movies use spiders to create creepy, crawly suspense. The bite of a black widow spider sounds serious—and it can be—but the creepy part is that you may not realize you have been bitten until you become ill.

Spiders are often blamed for all kinds of symptoms, from local itching to diffuse rashes. The fact is that spiders rarely bite humans, and in fact, most spider bites do not even break the skin with their bites.

The bites of very large spiders such as tarantulas can be painful. Otherwise, in the temperate regions, the only spiders to be feared are the black widow and the brown recluse.

• The black widow is a medium-sized spider whose body is about a half-inch long. The name is derived from the mistaken belief that the female invariably kills the male after mating. Two species are common to the United States.
  
  
  • The southern black widow has the shiny, black, globular abdomen with the distinctive red hourglass on the underside.
    
    
  • The northern black widow has a row of red spots down the middle of the upper surface of its abdomen and 2 crosswise bars on the undersurface. Just to make things interesting, the markings can also be yellow or white, and the spider itself may be brown or have red legs.
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• Black widow spiders are nocturnal and, thus, are active at night. They prefer dark corners or crevices. They are said to avoid human dwellings, but you can find them in such areas as outhouses and garages. Only the female black widow bites humans, and she bites only when disturbed.

The black widow spider produces a protein venom that affects the victim’s nervous system. Some people are slightly affected by the venom, but others may have a severe response. The first symptom is acute pain at the site of the bite though there may only be a minimal local reaction.

• The local pain may be followed by localized or generalized severe muscle cramps, abdominal pain, weakness, and tremor. In severe cases, nausea, vomiting, faintness, dizziness, chest pain, and respiratory difficulties may follow.
  
  
• The severity of the reaction can depend on the age and physical condition of the person bitten. Children and the elderly are more seriously affected than young adults.
  
  
• In some cases, abdominal pain may mimic such conditions as appendicitis or gallbladder problems. Chest pain may be mistaken for a heart attack.
  
  
• Blood pressure and heart rate may be elevated.
  
  
• People rarely die from a black widow's bite. Life-threatening reactions are generally seen only in small children and the elderly.

In general, treatment for serious reactions to a black widow spider's bite will be beyond the scope of most medical offices and urgent care centers. Pain relief may require the use of narcotics and antivenin (antitoxin to counteract the effects of the spider venom).

The decision to seek emergency care is usually easy and should be made early. If the person who was bitten by a black widow spider has more than minor pain or has whole-body symptoms, seek care at a hospital's Emergency Department. If symptoms are severe, call 911 for emergency medical transport so that evaluation and treatment can start en route to the hospital.

|Self-Care at Home|

The options for home care are somewhat limited. Both cold and warm compresses have been recommended, as have hot baths. Certainly, a hot bath would seem to be of value because the pain is due primarily to muscle spasm. Obviously, over-the-counter pain relievers such as acetaminophen and ibuprofen may be of value in mild cases. Folk remedies have not proven to work.

|Medical Treatment|

In general, extensive medical evaluation is not necessary. The exceptions are when the history of a black widow bite is not clear, if the bite was not witnessed, and when associated symptoms require the exclusion of more serious disorders, such as heart attack.

|Medications|

In general, the person bitten by a black widow spider, who has pain severe enough to seek treatment at an Emergency Department, will require narcotic pain relief. Muscle relaxants given by injection may also be of value. Although calcium gluconate given through an IV has long been advocated, it does not seem to produce much relief of symptoms.

Use of antivenin

The antivenin available for treatment of black widow spider bites is derived from horse serum. The venom produced by various species of spiders is similar, so the antivenin prepared against one venom is effective against the others. Antivenin is produced by gradually increasing injections of the specific venom in a horse. The horse naturally produces the antivenin used in humans.

Symptoms are often not easily relieved, even with narcotics. Some experts recommend that antivenin be used in any severe bite because 1 vial of the antitoxin produces significant and rapid relief of symptoms. It can even be used if there is delay in reaching the hospital. Yet other sources recommend that antivenin be used only in children, the elderly, and those with severe underlying medical conditions.

The obvious risk for using antivenin is allergic reaction to horse serum, and the bitten person must be skin-tested for this possibility. Although delayed serum sickness is common when horse serum is used to treat rattlesnake bites, it is uncommon when used to treat black widow spider bites (probably because of the low dose needed for relief).

Be aware, however, that this antivenin may not be readily available at most hospitals; there may be some delay or difficulty in obtaining it when needed.

Of interest: The use of the black widow antivenin might sensitize the person for later use of rattlesnake antivenin. Obviously, the physician should discuss lifestyle habits that might affect the person’s risk of incurring a snakebite in the future. In many areas, black widow bites are much more common than rattlesnake bites.

|Follow-up|

In general, follow-up is only necessary in cases where antivenin is used. Although serum sickness is uncommon with single-vial doses of horse serum, it may occur 7-12 days after exposure and is characterized by skin lesions, fever, pain in the joints, and swollen lymph glands. The symptoms may occur sooner in a sensitized person. The process is self-limited, goes away in 2-3 weeks, and may be treated with antihistamines and steroids.

|Prevention|

Because black widow spiders bite if they are disturbed, care should be taken in reaching into dark areas. This includes sitting down in an outhouse without first checking for other inhabitants. In areas where spider infestations are a problem, the use of a pest control service may also be useful.

|Outlook|

Complications in healthy adults are uncommon. If the black widow spider bite is not treated with antivenin, symptoms may last for several days but are seldom life threatening.

Author: Martin J Boyd, MD, Consulting Staff, Department of Emergency Medicine, Memorial Medical Center.

Editors: Scott H Plantz, MD, FAAEM, Research Director, Assistant Professor, Department of Emergency Medicine, Mount Sinai School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, ; Thomas Rebbecchi, MD, FAAEM, Program Director, Assistant Professor, Department of Emergency Medicine, University of Medicine and Dentistry of New Jersey.