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Species Latrodectus mactans - Southern Black Widow

Black Widow - Latrodectus mactans - female Latrodectus spp? - Latrodectus mactans Obviously Black Widow, but which one?? - Latrodectus mactans - female Southern Black Widow - Latrodectus mactans - male Male Southern Black Widow (Latrodectus mactans) - Latrodectus mactans - male Black Widow - Latrodectus mactans - female Black Widow - Latrodectus mactans Southern Black Widow - Latrodectus mactans - female
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Entelegynes )
Family Theridiidae (Cobweb Spiders)
Genus Latrodectus (Widow Spiders)
Species mactans (Southern Black Widow)
Other Common Names
Black Widow - The L. mactans is often considered the original "Black Widow".
“The Hourglass Spider” because of the red hourglass shaped mark on the female’s abdomen.
“The Shoe Button Spider” due to the form of the spider’s jet-black abdomen.
Pronunciation
lat"ro-dek't[schwa]s mac'·tans
Explanation of Names
Latrodectus mactans is a mixture of Latin and Greek for "murderous biting robber". (Net Ref. 3)

See the Latrodectus guide page for the etymology of Latrodectus.
Size
Adult Female:
     Approximately 8-13 mm (~1/2 inch) in body length.
     With legs extended, the female measures about 25-35 mm (1 inch - 1 1/2 inches).

Adult Male:
     Approximately half the size of the female, around 4-6 mm (1/4 inch) in body length.
     With legs extended, the male measures 12-18 mm (1/2 inch - 2/3 inch).
See this picture for side-by-side view:
Identification
The southern black widow is one of the most common of the native widow spiders. It is the epitome of the classic widow spider, occurring in all the normal widow spider habitats.

Female: The adult female black widow spider has a glossy jet black color all over, including body and legs. The only red marks are the bright red hourglass mark on the underside of the abdomen, and a red spot just behind and above the spinnerets. The hourglass marking consists of two connected red triangles on the underside. Note, however, that the hourglass color may range from yellowish to various shades of orange or red. If the hourglass marking is not connected (e.g. - two distinct, non-touching triangles), it is most likely the northern cousin (L. variolus) of the southern black widow (L. mactans)
   

Males: Adult males are harmless, is 3-5 mm long with an elongated abdomen. The male’s legs are larger than the female’s and each joint is orange brown in the middle and black on the ends. On the sides of the male’s abdomen there are four pairs of red and white stripes. (Net Ref (3))
   

Immatures: Newly hatched spiderlings are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Juveniles of both sexes resemble the male and are harmless. (Net Ref (1))
   

Egg Sacs:
   

Web
The web is typically a 3-dimensional, unorganized mass of silk spun in a dark crevice or corner. The web is sticky, and very strong. If the web is active (in use), the female will be in or very near the web.
Range
It ranges as far north as southern New York, as far south as Florida, and as far west as Texas, Oklahoma, and Kansas. (L. mactans has been found in California, possibly indicating that it can be found in any southern state.) The Southern black widow spider also occurs throughout all four deserts of the American southwest.

In addition, Latrodectus mactans has been found in parts of southern Canada.
Habitat
Outdoors, black widow spider webs are usually built in woodpiles, rubble piles, under stones, in hollow stumps, and in rodent burrows. These spiders commonly occur in outbuildings such as privies, sheds, and garages. Indoors, they prefer undisturbed, cluttered areas in basements and crawl spaces. It is also associated with littered areas, with dumps of large cities, with garages, and storage sheds.
Food
They typically prey on a variety of insects, but occasionally they do feed upon wood lice, diplopods, chilopods and other arachnids. When the prey is entangled by the web, L. mactans quickly comes out of its retreat, punctures and poisons its prey(1) The poison takes about 10 minutes to take effect, meanwhile the prey is held tight by the spider(1). When movements of the prey cease, digestive enzymes are released into the wound(1). The black widow spider then carries its prey back to its retreat before feeding(1).

Latrodectus mactans is exclusively carnivorous and antagonistic. Ordinarily it feeds on insects; however, it also consumes wood lice, diplopods, chilopods and other arachnids. Usually, the black widow spider enswathes prey caught in its snare, bites it, and later drags it to its hub, or retreat, to be eaten. Latrodectus mactans inflicts a small wound on its prey, uses its cheliceral teeth to mash it up, pours digestive enzymes on the prey; and sucks up the resulting food. The whole digestion process takes place outside the spider’s body.
Life Cycle
Mating takes place in spring or summer. Black widow spiders reproduce sexually where the male inserts his palpus into the female's spermathecal openings. The notion that female always eat the male after mating is incorrect! Females have been observed killing and eating the male after mating; however, a large majority of males do escape, especially when he doesn't remain around the web after mating, and the female is already well-fed.

The female lays eggs onto a web where they are camouflaged and guarded. A female black widow spider can produce nine egg sacs in one summer, each containing about 400 eggs . Usually, eggs incubate for 20-30 days, but more than 12 rarely survive through this process, due to cannibalism. 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 90 days.

Copulation among Latrodectus mactans is unique. A mature male spins a small “sperm web” and deposits a small quantity of semen on it. He then charges his palps with the sperm, abandons his habitat, and spends considerable effort to locate a female of his species. Once the female black widow spider has been located, courtship begins. The male vibrates the threads of the female’s snare to be sure she is the right species, for her to recognize him as a mate, and to make her receptive to mating. Mating takes place when the male inserts his papal organs into the spermathecal openings of the female. The spermatozoa are released onto the eggs. The female black widow spider’s egg sac is globular shaped (pear-shaped), and are about 1/3 to 1/2-inch diameter. Sacs are white at first, later turning tan or gray. The eggs are laid onto a small web and are covered with more silk until they are completely surrounded by an egg sac or cocoon. This egg sac is then camouflaged, guarded (while suspended in the web), or carried by the female. Within the egg sac, the eggs hatch and spiderlings (juveniles) emerge. The spiderlings hatch and molt (shed their skin) one time while inside the egg sac. They then disperse by ballooning—extruding silk threads and being transported by air currents. Their growth to maturity requires 2 to 4 months depending on the availability of prey. Spiderlings molt several times before reaching maturity. (Net Ref (3))

In addition, the female Latrodectus mactans can store a lifetime supply of sperm to fertilize all the eggs she will ever produce.

Internet References: (1), (3), and (4)
Remarks
Caution: This spider is venomous and can harm people. However, the female injects such a small dose of venom that it rarely causes death. Reports indicate human mortality at well less than 1% from black widow spider bites. (Net Ref (1))

While Latrodectus mactans is not aggressive and does not have the instinct to bite, her venom is neurotoxic, which means that it affects the transmission of nervous impulses. Black widow venom acts by causing a localized release of the neurotransmitter acetylcholine, which is involved in muscular contraction. A bite results in a severe, uncontrollable, and prolonged muscle contraction in the area of the bite.

If the black widow spider bites, most likely it has been pressed against human bare skin, and this causes a natural reaction, a bite in self-defense. For the most part, the black widow's bite may be felt only as a pin prick, during which the spider's fangs inject a minute amount of highly toxic venom under the skin. The severity of the victim's reaction depends on his or her age and health, and on the area of the body that is bitten. Local swelling and redness at the site may be followed in one to three hours by intense spasmodic pain, which can travel throughout the affected limbs and body, settling in the abdomen and back (intense abdominal cramping, described as similar to appendicitis), and can last 48 hours or longer. Elderly patients or young children run a higher risk of severe reactions, but it is rare for bites to result in death; only sixty-three having been reported in the United States between 1950 and 1959 (Miller, 1992). Other symptoms can include nausea and profuse perspiration. If left untreated, tremors, convulsions and unconsciousness may result. When death does occur, it is due to suffocation.

The Black Widow is considered the most venomous spider in North America, and it is reported that the venom of Latrodectus mactans is 15 times more toxic than a rattlesnake’s. (Net Ref (3))

For more general information about the Widow spider, please refer to the Latrodectus genus info page.

If you are bitten by a widow spp. spider:
Contact your physician, hospital or poison center immediately and follow their instructions. Poison Centers across the country now have a new national emergency phone number - 1-800-222-1222.
Collect the spider if possible for identification. Your physician may administer an antivenom treatment and calcium gluconate to alleviate pain, and will probably treat the site with antiseptic to prevent infection.
If you have a heart condition or are otherwise vulnerable, you may require a hospital stay until symptoms subside. Usually bite victims recover fully within two to five days.

Precautions:
Be very careful when working around areas where black widow spiders may be established. Take proper precautions-wear gloves and pay attention to where you are working. The reaction to a Black widow bite can be painful, and the victim should go to the doctor immediately for treatment.
See Also
Genus of False Widows (Steatoda): info
Specific Species of False Widow (Steatoda grossa): info
Internet References
2) Venomous Spiders in Florida: A detailed article by G. B. Edwards, Taxonomic Entomologist, Florida Dept of Agriculture & Consumer Services
3) University of Michigan Museum of Zoology: Animal Diversity Web: A nice, detailed yet simple discussion of animals, including the Southern Black Widow.
6) Desert USA - A very good guide for various dangers found within the desert.
7) Penn State Entomology Dept.: Some good, brief writeups about various spiders in PA, including the Black Widow.
Works Cited
1.Biology of Spiders
Rainer F. Foelix. 1996. Oxford University Press.