Tarantulas, tarantula articles 

Black widow spider

The black widow spider (Latrodectus mactans) is a spider notorious for its neurotoxic venom. It is a large widow spider found throughout the world and commonly associated with urban habitats or agricultural areas. Although the common name 'black widow spider' is used to refer specifically to L. mactans it is occasionally also applied to several members of the Latrodectus (widow spider) genus in which there are 31 recognized species including the Australian red-back and brown widow spider. In South Africa, the black widow is also known as the button spider.

Adult female black widow spiders are shiny black with an hourglass shape marking on the bottom of its abdomen which, although most commonly red, may range in color from white to yellow to various shades of orange and red. In some varieties, the two halves of the hourglass shape may be separated into two separate dots. Female black widow spiders are about 1.5 inches (38 mm) counting legspan. The body is about 0.5 inches (13 mm). Male black widow spiders are half the size of the female or smaller. They have longer legs and a smaller abdomen in relation to their body size. They are also usually dark brown with yellow stripes and a yellow hourglass mark. Juvenile black widow spiders are usually brown with yellow stripes and a yellow hourglass mark. Adult males can be distinguished from juvenile females by their more-slender body, longer legs and large pedipalps typical of most other male spiders.

Black widow spiders live in temperate and tropical zones (McCorkle, 2002). They typically prey on a variety of insects, but occasionally they do feed upon woodlice, diplopods, chilopods and other arachnids (McCorkle, 2002). 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 punctures and poisons its prey (Foelix, 1982). The venom takes about ten minutes to take effect, meanwhile the prey is held tightly by the spider (Foelix, 1982). When movements of the prey cease, digestive enzymes are released into the wound (Foelix, 1982). The black widow spider then carries its prey back to its retreat before feeding (Foelix, 1982).

As is characteristic of all arthropods, black widow spiders have a hard exoskeleton composed of chitin and protein (5). When a male is mature, he spins a sperm web, deposits semen on it, and charges his palpi with the sperm (3). Black widow spiders reproduce sexually when the male inserts his palpus into the female's spermathecal openings (3). The females often kill and eat the male after mating (hence the spider's name); however, some males do escape under circumstances wherein the female is already well-fed (1). The female deposits her eggs in a globular silken container which they remain camouflaged and guarded (3). A female black widow spider can produce nine egg sacs in one summer, each containing about 400 eggs (1). Usually, eggs incubate for twenty to thirty days, but rarely do more than twelve survive through this process, due to cannibalism (1). It takes two to four months for black widow spiders to mature. The female live on for 180 days after maturing, while a male only lives on for another ninety days (1).

Venom components and effects

Though its venom is extremely potent, little of it is injected and deaths from Latrodectus bites are rare, only sixty-three having been reported in the United States between 1950 and 1959 (Miller, 1992). Black widow venom acts by causing a localized release of the neurotransmitter acetylcholine, which is involved in muscular contraction.

There are a number of active components in the venom. There are a few high-molecular mass components (These proteins, called latrotoxins, cause a massive transmitter release from a diversity of nerve endings); a number of smaller polypeptides, toxins interacting with cation channels which display spatial structure homology. They can affect the functioning of calcium, sodium, or potassium channels. There are also a few even more simple molecules, adenosine (1), guanosine (2), inosine (3), and 2,4,6-trihydroxypurine (4). The mechanism of the venom relates to the toxin initially being carried by the lymphatic system until it reaches the blood stream. Once in the blood, the toxin is moved by the circulation and deposited in the nerve ends where they insert into the muscle. Most strongly affected are back, abdomen, and thigh muscle areas. The venom acts at the nerve ends to prevent relaxation of the muscle, causing tetany - or constant, strong, painful contractions of the muscles. Standard treatments usually involve symptomatic therapy with pain medication, muscle relaxants, and, rarely, antivenin. The venom does not typically cause problems at the bite site itself, unless a secondary skin infection occurs.

According to a widely-reported media story (Wigmore, 2003), Chilean scientists were using part of Latrodectus venom to synthesize a drug that will not only serve as a male contraceptive, but will also work in a fashion similar to Viagra; however, this has not been reported in any mainstream peer-reviewed scientific journal.

Widow spider

The widow spiders are members of the spider genus Latrodectus, a subset of the family Theridiidae. Latrodectus includes approximately 31 recognized highly poisonous species, with the black widow spiders (Latrodectus mactans) being the best known members of the group. Envenomation by these spiders can be fatal to children and ill or infirm adults. Ordinarily, the body mass of a healthy adult is sufficient to dilute the venom to less than a fatal concentration.

Spiders of the genus Steatoda (also of the Theridiidae family) are often mistaken for widow spiders, and are known as false widow spiders. The false widow spiders are significantly less harmful to humans.

Along with the Latrodectus mactans, the glossy black ones with the famed red hourglass, the gray or brown widow spiders (Latrodectus geometricus), the red widow spiders (Latrodectus bishopi), the northern widows (Latrodectus variolus), and the western widows (Latrodectus hesperus) (Preston-Malfham, 1998) are also found in the United States. But there are widow spiders on every continent of the world except for Antarctica. In some areas in Africa this Genus receives the generic name button spiders.

In common with other members of the Theridiidae family, the widow spiders construct a cobweb, i.e., an irregular tangle of sticky silken fibers. The black widow spider very frequently hangs upside down near the center of its web and waits there for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to bite it and swathe it in a silken shroud. If the spider feels threatened it will normally let itself down to the ground on a safety line of silk just as fast as it can. As with other web-weavers, these spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or warn them of larger animals that could injure or kill them. They are not aggressive, and most injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched somehow. It is possible that some bites may result when a spider mistakes a finger thrust into its web for its normal prey, but ordinarily intrusion by any large creature will cause these spiders to flee.


Range of Latrodectus species (widow spiders) worldwide

Do you like it?

Source: Wikipedia