Black Widow Spider

Latrodectus is a spider genus with many species that are collectively referred to as true widows. This classification includes spiders that are often referred to as black widow spiders, brown widow spiders, and related spiders. However, since the diversity of species is so wide, such broad "common names" are only of limited usage. This genus, a member of the Theridiidae tribe, includes 32 species, including some North American "black widows" (southern black widow Latrodectus mactans, western black widow Latrodectus hesperus, and northern black widow Latrodectus variolus). In addition to these in North America, there is the red widow Latrodectus bishopi and the brown widow Latrodectus geometricus, which has a much broader regional range. 

Other species include the European black widow (Latrodectus tredecimguttatus), the Australian redback black widow (Latrodectus hasseltii), some Southern African species such as Button spiders, and South American black widow spiders (Latrodectus corallinus and Latrodectus curacaviensis). The neurotoxin latrotoxin, which induces the disease latrodectism, is found in the venom of these small spiders, all of which are named after the species. Female widow spiders have extraordinarily large venom glands, and their bite can be especially dangerous to large vertebrates like humans. Only the females' bites are harmful to humans.

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Black Widow Spider - Description

Female black widow spiders are dark brown or glossy black when fully grown, with a red or orange hourglass on the ventral surface (underside) of the abdomen; others may have a pair of red spots or no markings at all. Male black widow spiders often have numerous red or red and white marks on the dorsal surface (upper side) of the abdomen, varying from a single line to bars or spots, and juveniles often resemble the male pattern. Females are mostly black in colour, but others can have lighter or even reddish bodies. Many have red, white, or brown marks on the upper (dorsal) side of the black widow belly(abdomen). Some are distinguished by reddish marks on the central underside (ventral) belly, which is often hourglass-shaped. Females in a few species are paler brown than males, and others lack bright markings. Do you know how long is a black widow spider?  Black widow spider ranges in size from 3–10 mm (0.12–0.39 in); some females can measure 13 mm (0.51 in) in length.

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Taxonomy

Charles Athanase Walckenaer founded the genus Latrodectus in 1805 for the species Latrodectus tredecimguttatus and Latrodectus mactans. Herbert Walter Levi, an arachnologist, revised the genus in 1959, examining the female sexual organs and recognizing their resemblance across described species. He argued that the colour differences were complex across the globe and insufficient to merit species classification, and reclassified the redback and many other species as subspecies of the black widow spider. Levi also stated that research on the genus had been contentious; in 1902, F. O. Pickard-Cambridge and Friedrich Dahl revamped the genus, each criticizing the other. Cambridge challenged Dahl's classification of species based on what he considered slight anatomical differences and the latter rejected the former as an "ignoramus."

Behaviour

The common name "widow spiders" comes from the prevalence of sexual cannibalism, a behaviour in which the female consumes the male after mating. This behaviour may increase the chances of offspring survival; however, females of certain species only rarely exhibit this behaviour, and much of the known evidence for sexual cannibalism has been found in laboratory cages where the males could not flee.

To prevent being eaten, male black widow spiders choose their partners by deciding whether the female has already eaten. They can detect whether or not the female has fed by detecting chemicals on the internet. 

Latrodectus hesperus is known as an "opportunistic cannibal" since it can turn to cannibalism in desperate circumstances. Latrodectus hesperus is known to partake in sibling cannibalism in addition to sexual cannibalism. Widow spiders, like other Theridiidae representatives, weave a web of irregular, intertwined, sticky silken fibres. Black widow insects tend to hide close to the ground in dark and undisturbed environments, normally in small holes made by animals or around building openings or woodpiles. Indoor nests are found in quiet, undisturbed areas such as under desks or chairs, or in basements. The spider sometimes hangs upside down at the centre of its web, waiting for insects to bumble in and get entangled. The spider then races over to envenomate and cover the bug in silk so it can escape. Tiny insects such as flies, mosquitoes, grasshoppers, bugs, and caterpillars are their prey. If the spider detects a threat, it easily lowers itself to the ground on a silk safety line. 

These black widow insects, like most web-weavers, have low eyesight and rely on movements hitting them across their webs to locate trapped prey or alert them of greater threats. When a widow spider is caught, it is unlikely to bite; instead, it will play dead or flip silk at the imminent threat; bites occur when they are unable to escape. 

The overall tensile strength and other physical properties of Latrodectus hesperus (western black widow) silk are comparable to those of orb-weaving spider silk measured in previous tests. In the Blackledge report, the tensile strength of the three types of silk tested was about 1,000 MPa. In a previous analysis, the ultimate strength of Trichonephila edulis was stated to be 1,290 160 MPa. Spider silk has a tensile strength equal to steel wire of the same thickness. However, since steel has a density approximately six times that of silk, silk is correspondingly stronger than steel wire of the same weight. Spiders of the family Steatoda (also of the Theridiidae) are often misidentified as widow spiders and are dubbed "false widow spiders"; although their bite can be unpleasant, they are much less dangerous to humans.

Distribution

In North America, the black widow animals are commonly known as southern (Latrodectus mactans), western (Latrodectus hesperus), and northern (Latrodectus variolus) are found in the United States, as well as parts of southern Canada – particularly in the Okanagan Valley of British Columbia, as can the "grey" or "brown widow spiders" (Latrodectus geometricus) and the "red widow spiders" (Latrodectus bishopi). Widow spiders can be found on any continent except Antarctica. 

The most widespread species in eastern Asia and Australia is known as the redback (Latrodectus hasselti).

Owing to their common appearance, they are often confused with spiders of the genus Steatoda, also known as false widow spiders.

Black Widow Spider Bite

Black widow bites are highly dangerous due to the prevalence of latrotoxin in their venom, which can cause systemic symptoms (latrodectism) such as extreme muscle pain, stomach cramps, hyperhidrosis, tachycardia, and muscle spasms. Symptoms typically last 3–7 days, but they can last for many weeks.

Allan Blair, a medical faculty member at the University of Alabama, performed an experiment in 1933 to track the effects of a black widow bite and to see whether anyone could develop immunity after being bitten. Blair refused to finish the procedure and did not consent to be bitten a second time because the results of the bite were so unpleasant and harsh. Every year, about 2,200 individuals in the United States report being attacked by a black widow spider, but the vast majority do not need medical attention. Any bites have no poison injected into them—this is known as a "dry" bite. Since 1983, no deaths from black widows have been confirmed to the American Association of Poison Control Centers in the United States. Black widow spiders are not particularly aggressive, and they seldom attack humans unless they are alarmed or otherwise threatened. Contrary to common opinion, most people who are bitten suffer only minor injuries, if any at all. In the early twentieth century, fatal bites were mainly reported from Latrodectus tredecimguttatus, the Mediterranean black widow. Since the poison is normally not life-threatening, antivenom has been used for pain control rather than saving lives. Research, however, found that when generic pain relief was paired with either antivenom or a placebo, it resulted in comparable changes in pain and symptom resolution.

Black Widow Spider Facts

• Black widow spiders are the most venomous spiders in North America, according to National Geographic. According to NCSU, their venom is 15 times heavier than that of a rattlesnake. Black widow spiders are very poisonous; thankfully, they only attack humans when they are disturbed.

• About the fact that sexual cannibalism is uncommon among black widows, males make every effort to avoid being post-coital snack. Male black widows check out well-fed virgins for breeding, according to a 2014 report published in Animal Behavior.