The widow spiders, genus Latrodectus, are among the most recognized spiders on earth; they are the largest of the cobweb weavers, family Theridiidae, and all species are poisonous. The term widow spider originated from the idea that the females devour the males after, or during, mating. This mate devouring behavior is somewhat a myth; while it may occur in captive situations, where the male cannot escape, it is uncommon in the field. There are five species in the United States, one in southern Europe, and additional species in Australia, the Near East, and South America. Widow spiders build strong, sloppy webs, in which the females usually remain, hanging upside down most of the time. Female widow spiders are bulbous and shiny in appearance, and may have bodies 12-16 mm long. Males are much smaller than the females, with longer legs; they are so different in appearance than females, that they are rarely recognized as widow spiders by the lay person; males are not considered a threat to humans, although they do possess venom and can bite. Juvenile widow spiders are usually light colored, and darken to their adult coloration gradually, with each successive molt of their exoskeleton.
The term black widow refers to those species in the United States, Europe, and some other areas, which are shiny black in appearance. The most well known of the U.S. black widows is the southern widow, Latrodectus mactans, whose latin name translates "murderous biting robber". The southern widow is found in the southeastern U.S., west to central Texas and Oklahoma, and north to southern New York; it is also found in the West Indies. Like most widow spiders, it prefers dark, cool places to build its web, such as outhouses, window wells, under well covers, and beneath trash. The red "hourglass" of the southern widow is actually shaped more like an anvil than a perfect hourglass in most specimens. The southern widow causes many envenomations in humans, particularly in the southern part of its range, where it is most common.
The western black widow, Latrodectus hesperus (photograph), ranges from extreme southwestern Canada, south into Mexico, and east to west Texas. Hesperus is the common black widow of the western United States, and is abundant in regions of Arizona, California, and other westerly locales. One of its favored natural habitats is in abandoned rodent holes, but it is often found around human habitations, even in the "downtown" districts of many western U.S. cities. The western widows' general appearance is very similar to that of the southern widow; the "hourglass" marking in the western widow is usually shaped like a perfect hourglass, though it is devided into two seperate "spots" in some specimens. Like its southern cousin, the western widow causes a large number of bites, particularly in the southern part of its range.
The northern widow, Latrodectus variolus, is the third black widow found in the United States. It is found from extreme southeastern Canada, throughout the New England states, and south to northern Florida. It prefers undisturbed wooded areas, stone walls, stumps, and similar habitats. The "hourglass" of the northern widow is usually devided into two separate, elongate markings. This species is most common in the northern part of its range. While its venom is very similar to that of the southern and western widows, and bites do occur, it does not appear to bite humans as often as those species.
The red widow, Latrodectus bishopi, is a U.S. species with a restricted range, being found only in palmetto fronds of sandy, scrub-pine regions of central and southern Florida. This spider is rather brightly colored, with red legs and cephalothorax (fore-part of the body), and a black abdomen with orange and white markings down the back and sides. The "hourglass" usually consists a single red elongate marking. Little is known of the bite of the red widow, but its venom is probably quite toxic to mammals.
The brown widow, Latrodectus geometricus, is a cosmotropical species, found in most tropical seaports around the world; it is an introduced species in Florida. Coloration may vary, but is usually brown to grey, with white and black markings on the back and sides of the dorsal abdomen: The "hourglass" is usually complete. This species is often found on or around human habitations and other buildings. While definitely venomous to humans, bites tend to be less severe than those of most other widow spiders.
The malmignatte, or European black widow, Latrodectus mactans tredecimguttatus, is the common widow spider of southern Europe (northern Mediterranean). It is black, with a series of red markings on the dorsal abdomen. The malmignatte is a significant medical problem in various parts of its range. In Herzegovina (the former Yugoslavia) this spider reportedly causes a large number of bites each autumn in field workers harvesting grain by hand.
The redback spider, Latrodectus mactans hasselti, is found throughout Australia, and in some Southeast Asian countries. It is black, with a distinct red (sometimes pink or light grey) marking on its dorsal abdomen. Like most widow spiders, it harbors a highly toxic venom, and is considered a species of clinical significance. Similar species are found in South Africa.
Bites by widow spiders often are initially painful, but sometimes are not felt. The local dermal reaction is minimal, usually consisting of little more than an area of erythema (redness) around the bite site, which disappears within several hours; no tissue necrosis occurs following bites by widow spiders. A potent neurotoxin in the venom induces the disease state latrodectism, which manifests itself with severe muscle cramping and spasms; the cramping usually begins in the large muscle masses of the legs, or the abdomen. The abdomen can exhibit a board-like rigidity, and the pain has been compared to that of acute appendicitis, and to childbirth. Some widow bite victims experience anxiety, profuse sweating, nausea, piloerection (hair standing on end), increased blood pressure, and other unpleasant manifestations. Paralysis, stupor and convulsions, as well as psychological abnormalities may occur in severe cases. Death can occur in a small percentage of cases, particularly when the victim is a small child or elderly person.
Persons bitten by widow spiders usually present themselves to medical facilities voluntarily, as a result of intense pain. The treatment for widow spider bites may vary, according to the age of the victim and the severity of the poisoning: The most common effective treatment is the intravenous administration of the muscle relaxant calcium gluconate, often requiring several courses of treatment to abate the cramping and spasms: Robaxin (Methocarbamol) has been used successfully in cases that did not respond well to calcium gluconate. Antivenin (antivenom or antivenene in some countries) is produced against the venom of widow spiders in Australia, Europe, South Africa, and the United States. It can be used in severe cases, which do not respond to muscle relaxant therapy, or where the victims life is compromised. As with most spiders, black (and other) widow spiders bite humans only in accidental situations: Widow spiders are practically blind, and spend most of their lives in the web.
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