Latrodectus mactans: Difference between revisions
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Although their venom is extremely potent (it is also reported to be much more potent than the venom of [[cobra]]s and [[coral snake]]s), these spiders are not especially large. Compared to many other species of spiders, their [[chelicerae]] are not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each [[chelicera]], the part that penetrates the skin, is approximately 1.0 millimeters (about .04 in) long, long enough to inject the venom to a point where it can be harmful. The males, being much smaller, inject far less venom with smaller chelicerae. The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of [[latrodectism]]). Deaths in healthy adults from ''Latrodectus'' bites are relatively rare in terms of the number of bites per thousand people. Sixty-three deaths were reported in the United States between 1950 and 1959<ref>Miller T. Latrodectism: bite of the black widow spider. American family physician 1992; 45:181-187 .</ref>. On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of their genus. Widow spiders have more potent venom than most spiders, and prior to the development of [[antivenin]], 5%<ref>Bettini S. Epidemiology of latrodectism. Toxicon 1964; 2:93-101.</ref> of reported bites resulted in fatalities. The venom can cause a swelling up to 15 cm. |
Although their venom is extremely potent (it is also reported to be much more potent than the venom of [[cobra]]s and [[coral snake]]s), these spiders are not especially large. Compared to many other species of spiders, their [[chelicerae]] are not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each [[chelicera]], the part that penetrates the skin, is approximately 1.0 millimeters (about .04 in) long, long enough to inject the venom to a point where it can be harmful. The males, being much smaller, inject far less venom with smaller chelicerae. The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of [[latrodectism]]). Deaths in healthy adults from ''Latrodectus'' bites are relatively rare in terms of the number of bites per thousand people. Sixty-three deaths were reported in the United States between 1950 and 1959<ref>Miller T. Latrodectism: bite of the black widow spider. American family physician 1992; 45:181-187 .</ref>. On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of their genus. Widow spiders have more potent venom than most spiders, and prior to the development of [[antivenin]], 5%<ref>Bettini S. Epidemiology of latrodectism. Toxicon 1964; 2:93-101.</ref> of reported bites resulted in fatalities. The venom can cause a swelling up to 15 cm. |
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Improvements in plumbing have greatly reduced the incidence of bites and fatalities in areas where outdoor privies have been replaced by flush |
Improvements in plumbing have greatly reduced the incidence of bites and fatalities in areas where [[outhouse|outdoor privies]] have been replaced by [[flush toilet]]s. |
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There are a number of active components in the venom: |
There are a number of active components in the venom: |
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Revision as of 18:08, 20 November 2008
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The black widow spider is a group of spiders which includes the southern black widow (Latrodectus mactans), the northern black widow (Latrodectus variolus), and the western black widow (Latrodectus hesperus). As the name indicates, the southern widow is primarily found in (and is indigenous to) the southeastern United States, ranging from Florida to New York, and west to Texas, Oklahoma and Arizona, where they run particularly rampant. The northern black widow is found primarily in the northeastern United States and southeastern Canada, though its ranges overlap that of L. mactans quite a bit. The western widow is found in the western United States, as well as in southwestern Canada and much of Mexico. Black widows range in the southern parts of British Columbia, Alberta, Manitoba and Ontario - but only on the Bruce Peninsula.[1] They are often confused with the False Black Widows.
Prior to 1970, when the current taxonomic divisions for North American black widows were set forth by Kaston[2], all three varieties were classified as a single species, L. mactans. As a result, there exist numerous references which claim that "black widow" (without any geographic modifier) applies to L. mactans alone. Since common usage of the term "black widow" makes no distinction between the three species (and many people are unaware of the differences between them), and because the three species have much in common, this article treats all three species of black widow equally. Except where otherwise indicated, the remainder of the article applies to all three of the above species.
Black widow spiders typically prey on a variety of insects, but occasionally they do feed upon woodlice, diplopods, chilopods and other arachnids.[3] When the prey is entangled by the web, L. mactans quickly comes out of its retreat, wraps the prey securely in its strong web, then bites and envenoms its prey. The venom takes about ten minutes to take effect; in the meantime, the prey is held tightly by the spider. When movements of the prey cease, digestive enzymes are released into the wound. The black widow spider then carries its prey back to its retreat before feeding.[4]
Venom
Although their venom is extremely potent (it is also reported to be much more potent than the venom of cobras and coral snakes), these spiders are not especially large. Compared to many other species of spiders, their chelicerae are not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1.0 millimeters (about .04 in) long, long enough to inject the venom to a point where it can be harmful. The males, being much smaller, inject far less venom with smaller chelicerae. The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of latrodectism). Deaths in healthy adults from Latrodectus bites are relatively rare in terms of the number of bites per thousand people. Sixty-three deaths were reported in the United States between 1950 and 1959[5]. On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of their genus. Widow spiders have more potent venom than most spiders, and prior to the development of antivenin, 5%[6] of reported bites resulted in fatalities. The venom can cause a swelling up to 15 cm. Improvements in plumbing have greatly reduced the incidence of bites and fatalities in areas where outdoor privies have been replaced by flush toilets.
There are a number of active components in the venom:
- Latrotoxins
- A number of smaller polypeptides - toxins interacting with cation channels which display spatial structure homology - which can affect the functioning of calcium, sodium, or potassium channels.
- Adenosine
- Guanosine
- Inosine
- 2,4,6-trihydroxypurine.
The venom is neurotoxic.[7]
- ^ "Black widows in Ontario? Absolutely, but only on the Bruce Penninsula." - John Acorn, Bugs of Ontario, page 147
- ^ Kaston, B. J. (1970). "Comparative biology of American black widow spiders". Transactions of the San Diego Society of Natural History. 16 (3): 33–82.
- ^ Latrodetus Mactans McCorkle, Matthew. October 17, 2002.
- ^ Foelix, R. (1982). Biology of Spiders, pp. 162-163. Harvard University, U.S.
- ^ Miller T. Latrodectism: bite of the black widow spider. American family physician 1992; 45:181-187 .
- ^ Bettini S. Epidemiology of latrodectism. Toxicon 1964; 2:93-101.
- ^ Cite error: The named reference
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