Introduction
Background
The black widow, or hourglass, spider is the most dangerous species in the United States because of its potent venom. Spiders of the genus Latrodectus are worldwide in distribution. In the United States, they are found in every state except Alaska. They are predominantly observed in southern and western states. Five species of widow spiders are extant in the United States.
Spiders of the Latrodectus genus are not aggressive, biting only when disturbed. Black widow spiders spin webs and await their prey. They can usually be found in their webs, which are often located near protected places, such as the undersides of stones and logs; in the angles of doors, windows, and shutters; and in littered areas such as city dumps, garages, barns, outhouses, and sheds. Often, these webs are found around outdoor toilet seats, resulting in bites on or near the genitalia.
Adult females are mostly jet-black and often have striking red markings on their abdomens. On the ventral surface of the globular abdomen is a characteristic marking that consists of 2 equilateral triangles arranged apex to apex in an hourglass configuration.
Black widow spider. Reprinted with permission from Cutis 1995; 56: 257.
Black widow spider (Latrodectus mactans) with egg sac. Photo by Sean Bush, MD.
Black widow spider (Latrodectus mactans) and offspring. Photo by Sean Bush, MD.
For an ophthalmological perspective, see Spider Bites.
Pathophysiology
The venom of the black widow is a neurotoxin. It primarily causes systemic symptoms with little local damage at the bite site and no local necrosis. The venom mediates its effects through an initial release of massive amounts of acetylcholine at neuromuscular junctions. Latrotoxin is specific to nerve terminals; no direct release of transmitters from the adrenal medulla has been shown. As depolarization of the membrane occurs, a Ca++ -dependent release of neurotransmitters down the concentration gradient ensues. Reuptake of the neurotransmitters appears to be blocked as well.
Frequency
United States
The incidence of envenomation from black widow spiders is unknown. In Texas, 760 black widow spider bites were documented from 1998-2002, with an increased prevalence in western Texas.1 Black widow spiders can travel. One presumably did so in a packaged dishwasher shipped from Mexico to Michigan, resulting in a bite producing serious health consequences.2
Mortality/Morbidity
More than 13,000 spider bites were reported to the American Association of Poison Control Centers in 1997, with no deaths; more than 1,300 of the bites were described as moderate or severe.3 The reported death rate from documented bites occurs in less than 1% of reported cases. Young children appear to be at highest risk for a lethal bite.Age
Envenomation can occur in people of any age. The very young, the very old, and persons with cardiovascular disease are at increased risk for complications.
Clinical
History
Envenomation can occur in people of any age. Initially, a severe pain in local muscle groups occurs, which then spreads to regional muscle groups. Severe cramps and contraction of musculature may extend throughout the body. The abdominal pains are frequently most severe, mimicking appendicitis, colic, or food poisoning. Other symptoms include headache, restlessness, anxiety, fatigue, and insomnia.
Physical
Signs of latrodectism include salivation, lacrimation, diaphoresis, tremors, tachycardia, bradycardia, hypertension, shock, and coma. Slight erythema, piloerection locally, mild edema or urtication, local perspiration, and lymphangiitis are the primary local features that may be present. Myocarditis may occur, possibly with an ST-segment elevation and accompanying augmentation in T-wave amplitude after black widow spider envenomation.4,5 Potentially fatal cardiac involvement should be considered.
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| References |
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References
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Further Reading
Keywords
black widow spider bite, black widow spider, spider bite, Latrodectus mactans bite, L mactans bite, hourglass spider bite, neurotoxin, latrotoxin, salivation, lacrimation, diaphoresis, latrodectism
