Black widow spider

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Adult female black widow spider

The black widow spiders (genus Latrodectus), also sometimes referred to as shoe-button spiders or hourglass spiders, are a group of 32 known extant species of small, black, globose, and highly venomous arachnids that inhabit temperate and warmer climate areas throughout the world. They are especially dense in the American South and Southwest and in Australia. Females of some species may be between 2 and 2.5cm (about 1 inch) in length.[1] They are so named from the habit occasionally observed in females of consuming the male as a prey item directly following copulation in an act of sexual cannibalism (such behavior, however, is not unusual in many spider and other arthropod genera, including, for example, many species of jumping spider and praying mantis). The adult female of the most familiar black widow spider species is readily identified by a usually bright-red hour-glass shaped patch of chitin on the underside of its otherwise shiny black abdomen.

Immature female black widow, probably L. hesperus

Immature females lack this characteristic, but are also highly venomous and are identified by a colorful red, brown, and beige pattern on the dorsal side of the abdomen. Females of other species are identified by patterns of red dots on the dorsal side of the abdomen or by patterns of red dots and white stripes in this same place. Only females are of medical concern, as the shorter, weaker jaws of the males cannot penetrate mammalian skin.[2]

The neurotoxin of these spiders is, by volume, considered among the most toxic produced in nature, and by volume is more toxic than most snake venom. It is 15 times more virulent than that of the prairie rattlesnake.[3] A black widow can control the volume of poison it injects into its prey with a given bite, adjusting the amount according to prey size. The LD50 volume for humans for this toxin is between 0.43 and 1.39mg/kg, which is more than a single spider can usually produce, but is considered more than enough to kill a small dog or cat and is still enough to occasionally create a life-threatening condition in some people. As dogs and cats are usually covered in a protective layer of hair, black widow bites among them are relatively rare, though when bitten cats in particular are extremely vulnerable to the spider's poison as are horses and camels, and dogs are more sensitive to the poison than humans (because of the rarity of these bites and the inability of even veterinary specialists to identify such a bite in an animal, formal diagnosis is rare, and as veterinary clinics seldom stock the expensive antivenin, a diagnosis in an animal, even if correctly made, is seldom treatable). The exposed skin of humans is more subject to such bites, and about 2,500 are reported in the United States annually; in Australia, the number of bites reported to poison centers is often as much four times higher, despite a much smaller overall human population.[4]

Female spiders are often 20 times the mass of the males of the same species and produce much more venom than the other sex. Black widows will only attempt to bite a non-prey object if they feel threatened, preferring to hide whenever possible. Annual fluctuations in venom toxicity appear to show that toxicity is highest in autumn and lowest in spring. About one in eight bites on humans contains no venom at all.[2]

Adult male L. hesperus; dull light brown coloration such as this is typical of all male Latrodectus species

Both sexes of all black widows spider species build haphazard funnel-shaped webs in dark, secluded, dry, still areas such as basements, under eaves, in leaf piles, or around enclosed outdoor plumbing or along fence lines where they can find protection from wind, sun, and rain. Outhouses used to be especially convenient habitats, and a large proportion of black widow spider bites in the United States used to occur in them, specifically to men: the confused spider would bite the man's penis as he sat to use the facility.[5] Populations of these spiders often achieve high density near to human habitation where evening lights attract insect prey in large numbers, even though the spiders themselves eschew such lights; decomposing garbage or sewage may add to the draw for many insects.[2]

Unlike other kinds of typical spider wounds, there are normally no signs of tissue destruction at the site of a black widow spider bite. Symptoms of a bite, however, include cramping of large muscle areas, abdominal rigidity without tenderness, restlessness, hypertension, numbness in the region of the bite, and excessive salivation. Symptoms last for between three and six days, though the general weakness and sense of malaise following a bite can last for weeks or even months. Evidence of a bite can be obtained from urinalysis if conducted soon after the bite occurs. If diagnosed, treatment may include Acalatro or another antivenin administered as an intravenous drip (IV).[2]

Spiders within the group include:

See also[edit]


  1. ^ Measurement includes extended legs
  2. ^ a b c d Michael Edward Peterson; Patricia A. Talcott (29 November 2012). Small Animal Toxicology. Elsevier Health Sciences. p. 817. ISBN 1-4557-0717-1. 
  3. ^ Laurence Monroe Klauber (1997). Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind. University of California Press. p. 821. ISBN 978-0-520-21056-1. 
  4. ^ Helmut Greim; Robert Snyder (15 April 2008). Toxicology and Risk Assessment: A Comprehensive Introduction. John Wiley & Sons. p. 643. ISBN 978-0-470-86894-2. 
  5. ^ Pamela Nagami (1 September 2005). Bitten: True Medical Stories of Bites and Stings. St. Martin's. p. 28. ISBN 978-1-4668-2764-6.