| Latrodectus | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Arachnida |
| Order: | Araneae |
| Family: | Theridiidae |
| Genus: | Latrodectus Walckenaer, 1805 |
| Species | |
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Approx. 31, see article |
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Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten after mating, and can go on to fertilize other females.[1] The black widow spiders are perhaps the best-known members of the genus. The injection of neurotoxic venom latrotoxin from these species is a comparatively dangerous spider bite, resulting in the condition latrodectism, named for the genus. The female black widow's bite is particularly harmful to humans because of its unusually large venom glands; however, Latrodectus bites rarely kill human beings if their wounds are given medical treatment.
The prevalence of sexual cannibalism in Latrodectus by a female spider had given them the common name "black widow spider". The female Latrodectus most of the time eat their male Latrodectus partners after mating. As published in Times of India, The Researchers at the University of Hamburg in Germany found that male orb-web spiders make this ultimate evolutionary sacrifice for the good health of his offspring.[2]
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Not all adult female black widows exhibit the red hourglass on the ventrum or underside of the abdomen — some may have a pair of red spots or have no marking at all. Female black widows often exhibit various red markings on the dorsal or top side of the abdomen, commonly two red spots. However, it is believed that black widow young have at least some sort of marking on their abdomens. Adult male black widows are a quarter the size of the female, and are usually gray or brown rather than black and red; while they may sometimes have an hourglass marking on their ventral abdomen, it is usually yellow or white, not red. The bite of a male black widow is not considered dangerous to humans; it is the bite of the adult female black widow from her much larger venom sacs that has given this spider its dangerous reputation. While there is great variation in specifics by species and by sex, any spider exhibiting a red hourglass or a pair of large red round spots on the ventral abdomen with an otherwise black shiny body is an adult female black widow. The bright red hourglass & spots are never located on the dorsum, which is the more visible aspect; the identifying features are on the underside, anatomically known as ventrum ; ie, the spider must be lying on its back to reveal the markings.
Spiders of the genus Steatoda (also of the Theridiidae family) are often mistaken for widow spiders, and are known as "false widow spiders"; they are significantly less harmful to humans.
In common with other members of the Theridiidae family, the widow spiders construct a web of irregular, tangled, sticky silken fibers. The spider very frequently hangs upside down near the center of its web and waits for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to bite it and wrap it in silk. If the spider perceives a threat, it will quickly let itself down to the ground on a safety line of silk. As other web-weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats. While there are some more aggressive species, most are not; many injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched. Some bites are thought to result from a spider mistaking a finger thrust into its web for its normal prey, or in cases where a female is protecting an egg sac, but ordinarily intrusion by any large creature will cause these spiders to flee.
Silk from L. hesperus spiders is reputed to be particularly strong compared with the silk of other spiders.[3][4] However, the results of a study by Blackledge, et al. do not confirm this.[5]
The ultimate tensile strength (ultimate strength) (or tensile strength), and other physical properties of Latrodectus hesperus (western black widow) silk were found to be similar to the properties of silk from orb-weaving spiders that had been tested in other studies. The tensile strength for the three kinds of silk measured in the Blackledge study was about 1000 MPa. The ultimate strength reported in a previous study for Nephila edulis was 1290 MPa ± 160 MPa.[6] The tensile strength of spider silk is comparable to that of steel wire of the same thickness.[7] However, as the density of steel is about six times that of silk,[8] silk is correspondingly stronger than steel wire of the same weight.
The southern black widow, as well as the closely related western and northern species which were previously considered the same species, has a prominent red hourglass figure on the underside of its abdomen. Many of the other widow spiders have red patterns on a glossy black or dark background, which serve as a warning. Spiders which are found in multiple regions are listed in their predominant native habitat.
Widow spiders can be found on every continent of the world except Antarctica. In North America, the black widows commonly known as southern (Latrodectus mactans), western (Latrodectus hesperus), and northern (Latrodectus variolus) can be found in the United States, as can the "gray" or "brown widow spiders" (Latrodectus geometricus) and the "red widow spiders" (Latrodectus bishopi) (Preston-Malfham, 1998). The single species occurring in Australia is commonly called the redback (Latrodectus hasselti). African species of this genus are sometimes known as button spiders.
The following widow spiders are indigenous to North America:
The following are indigenous to Central and South America:
The following widows indigenous to the Mediterranean region, as well as in western Asia:
Media related to Latrodectus at Wikimedia Commons Data related to Latrodectus at Wikispecies
Other common names: Black Widow, Brown Widow, Red Widow.