The shiny black body and legs of the Southern Black Widow (Latrodectus mactans) are striking. The globose abdomen is typically decorated on its underside with a red hourglass-shaped marking. In some individuals, the hourglass may be separated into two parts and in young females, especially, there may be a row of red spots extending down the upper side of the abdomen (the slightly larger Northern Black Widow, L. variolus, which has an overlapping distribution but is more common in the northern part of its range, nearly always has these dorsal spots and the hourglass marking in two parts). The much smaller male has a more red-orange hourglass marking and a continuous or broken red-orange stripe bordered by white down the dorsal midline of the abdomen, as well as several pairs of diagonal white stripes along the sides of the abdomen. Young females often show a pattern similar to that of males. Female length is around 8 to 10 mm, but males are only 3.2 to 4 mm long.
The Southern Black Widow makes an irregular web of very strong and coarse silk, usually near the ground around tree stumps, in woodpiles, under stones and loose bark, around water faucets, in holes in the ground, and in garages, barns, storage buildings, and outhouses. When possible, it will retreat in the presence of a human interloper. Often the egg sac can be seen within the irregular web, guarded by the female. The nearly spherical egg sac is white to light brown, around 10 to 12 mm in diameter, and pear-shaped or with a distinctive nipple-like protrusion at the top.
Although the Southern Black Widow is widely distributed in North America and can supposedly be found in every U.S. state except Alaska, it is more common east of Kansas, Oklahoma, and Texas and especially in the southeastern United States, where most reported human fatalities have occurred. Most people who are bitten by these spiders have accidentally trapped the spider against their body or touched the web. The bite of the female contains a potent neurotoxin. Two red puncture marks can often be seen at the bite site and there is often a dull numbing pain around this area which may persist for 48 hours. This may be accompanied by abdominal pain, muscle cramps and spasms, and other serious symptoms. Shock and paralysis can occur. Reportedly, four to five percent of untreated bites lead to death. Thus, anyone bitten by a black widow should seek professional medical attention immediately. Vetter and Isbister (2008) provide a recent review of medical aspects of spider bites.
(Kaston 1978; Howell and Jenkins 2004)
- Howell, W.M. and R.L. Jenkins. 2004. Spiders of the Eastern United States: a Photographic Guide. Pearson Education, Boston.
- Kaston, B.J. 1978. How to Know the Spiders, 3rd edition. Wm. C. Brown Company, Dubuque, Iowa.
- Vetter, R.S. and G.K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology 53: 409-29.
Within the United States, Latrodectus mactans ranges as far north as Massachusetts and New Hampshire, as far south as Florida, and as far west as California, Texas, Oklahoma and Kansas. The black widow spider also occurs throughout all four deserts of the American southwest. In addition, Latrodectus mactans is found in Canada, Mexico, the West Indies, and South America.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
- Comstock, J. 1948. The Spider Book. Ithaca, New York: Comstock Publishing.
- Emerton, J. 1961. The Common Spiders of the United States. New York: Dover.
- Milne, L., M. Milne. 1990. The Audubon Society Field Guide to North American Insects. New York: Alfred A. Knopf, Inc..
- Shuttlesworth, D. 1959. The Story of Spiders. Garden City, New York: Doubleday & Company, Inc..
- Smith, R. 1980. Ecology and Field Biology. New York: Harper & Row Publishers.
- Desert USA Magazine, 2004. "Black Widow Spiders" (On-line). Accessed February 28, 2002 at http://www.desertusa.com/july97/du_bwindow.html.
Regularity: Regularly occurring
Type of Residency: Year-round
Latrodectus mactans is the largest spider of the family Theridiidae. The black widow spider is shiny, coal black in color. The female averages 8-10 mm in length and has long slender legs and a round abdomen. Usually on the underside of the female’s abdomen (venter) is a red hourglass mark and one or two red spots over the spinnerets and along the middle of her back. The male is 3-4 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. Young spiderlings, or juveniles, are orange, brown and white; they acquire their black coloring with age, or with each molt. (Emerton, 1961; Milne, 1990; Comstock, 1948; Kaston, 1953)
Another important characteristic of Latrodectus mactans is its “comb foot.” The spider has a row of strong, curved bristles on the hind pair of legs, which form a distinct comb. The comb is used for flinging silk over its prey. (Shuttlesworth, 1959; Comstock, 1948)
Average mass: 1 g.
Average length: 3-10 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; venomous
Sexual Dimorphism: female larger
A terrestrial environment is the habitat of the Latrodectus mactans. It is ubiquitous and builds strong-walled retreats quite close to the ground and in dark sheltered spots. However, it also spreads its snares over plants. Webs of the black widow spider can be found in recesses under stones or logs in a woodpile, in crevices or holes in dirt embankments, in barns and outbuildings. They can also be found around lids of dust bins, around seats of outdoor privies, spaces under chips of wood, around stacked materials of any kind, in deserted animal burrows or rodent holes, and entwined in grape arbors. This spider may find its way into clothing or shoes and occasionally seeks a spot in a house to build a web, but it is usually not found indoors. When it does seek shelter in a building, it is due to cold weather and a need for a dry shelter. In addition, in the eastern United States, Latrodectus mactans is associated with littered areas, with dumps of large cities, with garages, and storage sheds. In arid parts of Arizona, this spider inhabits almost every crevice in the soil and its nests are found in cholla cacti and agave plants. (Ferrand, 1988; Kaston, 1953; Preston-Mafham, 1984; Comstock, 1948; Gertsch, 1979; Shuttlesworth, 1959; Snow, 1970; Smith, 1980; Emerton, 1961; “Black Widow Spider, www.nscu.edu)
Biomes: temperate and tropical zones, including temperate forest, tropical rainforest,
temperate grassland, chaparral, desert
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: desert or dune ; chaparral ; forest ; rainforest
Other Habitat Features: urban ; suburban ; agricultural
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. (Kaston, 1953; Snow, 1970; Preston-Mafham, 1996; Foelix, 1996; Levine and Miller, 1991; Gertsch, 1979)
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
The black widow spider creates its own habitat wherever it spins its own web. With the aid of its web, the spider plays an active role in the ecosystem by helping to control insect populations.
Ecosystem Impact: creates habitat
A known predator is the mud-dauber wasp (Desert USA Magazine, 2004). The black widow spider spins a web which acts as a defense mechanism against predators. When a possible predator comes in contact with the web, it becomes entangled in the threads allowing the spider to wrap more silk around it and then inject it with its poison. Also, the female spider hangs upside down in her web so that her red hourglass mark serves as a warning signal to a predator (Farrand, 1988).
- mud-dauber wasps (Chalybion californicum)
Anti-predator Adaptations: aposematic
- Farrand, J. 1988. Familiar Insects and Spiders. New York: Chanticleer Press.
This list may not be complete but is based on published studies.
Known prey organisms
This list may not be complete but is based on published studies.
Life History and Behavior
Once the female produces her egg sacs she guards them until the spiderlings hatch. Once the spiderlings have hatched they leave the web (Milne, 1990).
Most spiders live for one year. Some are known to have lived 3 years in the wild, and in captivity, widow spiders may live for at least four years.
Status: wild: 3 years.
Status: captivity: 4 (high) hours.
Status: wild: 1 years.
Mating System: monogamous
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 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 saw is then camouflaged, guarded, or carried by the female. Within the egg sac, the eggs hatch and spiderlings (juveniles) emerge. The female black widow spider’s egg sac is pear-shaped. In addition, the female Latrodectus mactans can store a lifetime supply of sperm to fertilize all the eggs she will ever produce. (Hillyard, 1994; Snow, 1970; Kaston, 1953; Wallace et al, 1991; Foelix, 1996)
Breeding season: spring
Range number of offspring: 10 to 917.
Range gestation period: 8 to 30 days.
Average gestation period: 20 days.
Range : 2 to 6 months.
Average : 3 months.
Range age at sexual or reproductive maturity (female): 70 to 90 days.
Range age at sexual or reproductive maturity (male): 70 to 90 days.
Key Reproductive Features: seasonal breeding ; sexual ; fertilization (Internal ); sperm-storing
The female rarely leaves the web. She watches over the eggs in the egg sac until the spiderlings hatch. The spiderlings disperse soon after hatching, at which time parental care ceases and the spiderlings must fend for themselves.
Parental Investment: no parental involvement; female parental care
Molecular Biology and Genetics
Barcode data: Latrodectus mactans
There are 5 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Latrodectus mactans
Public Records: 2
Specimens with Barcodes: 8
Species With Barcodes: 1
Black widow spiders are fairly common and they are afforded no special conservation protections.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
NatureServe Conservation Status
Rounded Global Status Rank: GNR - Not Yet Ranked
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
While Latrodectus mactans are not aggressive and do not have the instinct to bite, their venom is neurotoxic, which means that it blocks the transmission of nerve impulses. 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. A bitten human suffers from a painful rigidity in the abdominal wall muscles. While the poison from this spider is serious, it is rarely fatal. If treated properly and promptly, the victim completely recovers. A black widow's bite is distinguished by a double puncture wound. Children and adults who are not in good physical condition suffer the most from the bite. It is reported that the venom of Latrodectus mactans is 15 times more toxic than a rattlesnake’s.
Negative Impacts: injures humans (bites or stings, venomous )
- Gertsch, W. 1979. American Spiders. New York: Van Nostrand Reinhold.
- Preston-Mafham, K., R. Preston-Mafham. 1996. The Natural History of Spiders. Ramsbury, Marlborough: The Crowood Press Ltd..
Economic Importance for Humans: Positive
On the positive side, Latrodectus mactans consumes enormous numbers of harmful insects. It gets rid of troublesome flies and mosquitoes,which carry diseases, as well as locusts and grasshoppers, which destroy grain crops. In addition, this spider ingests beetles and caterpillars, which defoliate plants and trees. The black widow’s entrapment of pests makes it invaluable to man and helps to balance nature. (Kaston, 1953; Shuttlesworth, 1959; Preston-Mafham, 1984) Furthermore, the silk and venom Latrodectus mactans produces has potential uses in biotechnology. Its venom could lead to a new generation of environmentally safe insecticides that leave no residues. Drugs derived from its venom may be able to save lives of future heart attack victims by means of an immediate effect on the blood vessels, allowing the blood to flow more easily.
Positive Impacts: source of medicine or drug ; controls pest population
- Hillyard, P. 1994. The Book of the Spider. New York: Random House, Inc..
- Kaston, B. 1953. How to Know the Spiders. Dubuque, Iowa: Wm. C. Brown Company.
- Preston-Mafham, K., R. Preston-Mafham. 1984. Spiders of the World. New York: Blandford Press Ltd..
Latrodectus mactans, or Southern black widow or simply black widow, is a highly venomous species of spider in the genus Latrodectus. They are well known for the distinctive black and red coloring of the female of the species and for the fact that she will occasionally eat her mate after reproduction. The species is native to North America. The venom is seldom fatal to healthy humans.
Latrodectus mactans was first described by Johan Christian Fabricius in 1775, placing it in the genus Aranea. It is currently placed amongst the Theridiidae family of the order Araneae. The species is closely related to Latrodectus hesperus (western black widow) and Latrodectus variolus (northern black widow). Members of the three species are often confused with the genus Steatoda, the False Widows. Prior to 1970, when the current taxonomic divisions for North American black widows were set forth by Kaston, all three varieties were classified as a single species, L. mactans. As a result, there exist numerous references which claim that "black widow" (without any geographic modifier) applies to L. mactans alone. Common usage of the term "black widow" makes no distinction between the three species.
The mature female is around 1.5 in (38 mm) long and 0.25 in (6.4 mm) in diameter. She is shiny and black in color, with a red marking in the shape of an hourglass on the ventral (under) side of her very rounded abdomen. There is much variation in female size, particularly in egg-carrying (gravid) females. The abdomen of a gravid female can be more than 0.5 in (~1.25 cm) in diameter. Many female widows also have an orange or red patch just above the spinnerets on the top of the abdomen.
The male is either black, or closer to the appearance of the juveniles in color, and is much smaller with a body of less than 1/4 inch (< 0.75 cm).
Juveniles have a distinctly different appearance to the adults, the abdomen is grayish to black with white stripes running across it and is spotted with yellow and orange.
The southern widow is primarily found in (and is indigenous to) the southeastern United States, ranging from Florida to New York, and west to Texas, Oklahoma, Arizona, and Nevada The northern black widow (L. variolus) is found primarily in the northeastern United States and southeastern Canada, though its range overlaps with that of L. mactans. In Canada, black widows range in the southern parts of British Columbia, Alberta, Saskatchewan, Manitoba and Ontario. In the Dominican Republic it is found along the whole country.
Latrodectus mactans, along with Latrodectus hesperus and Latrodectus geometricus (the "brown widow spider"), is established in the Hawaiian Islands (USA). One pathway of entry into Hawaii for at least one of these black widow species is imported produce (which is also considered an important potential pathway for widow spiders elsewhere).
When a male is mature, he spins a sperm web, deposits semen on it, and charges his palpi with the sperm. Black widow spiders reproduce sexually when the male inserts his palpus into the female's spermathecal openings. The female deposits her eggs in a globular silken container in which they remain camouflaged and guarded. A female black widow spider can produce four to nine egg sacs in one summer, each containing about 100–400 eggs. Usually, eggs incubate for twenty to thirty days. It is rare for more than a hundred to survive this process. On average, thirty will survive through the first molting, because of cannibalism, lack of food, or lack of proper shelter. It takes two to four months for black widow spiders to mature enough to breed, however full maturation typically takes six to nine months. The females can live for up to five years, while a male's lifespan is much shorter. The female, on occasion, eats the male after mating. Lifespans depend upon environment, with shelter being the greatest determining factor and food the second greatest. Males that escape being consumed by the females can go on to fertilize other females. It is a widely held misconception that females eat males after every mating.
Black widow spiders typically prey on a variety of insects, but occasionally they do feed on woodlice, diplopods, chilopods and other arachnids. When the prey is entangled by the web, Latrodectus mactans quickly comes out of its retreat, wraps the prey securely in its strong web, then bites and envenoms its prey. The venom takes about ten minutes to take effect; in the meantime, the prey is held tightly by the spider. When movements of the prey cease, digestive enzymes are released into the wound. The black widow spider then carries its prey back to its retreat before feeding.
Natural enemies 
There are various parasites and predators of widow spiders in North America, though apparently none of these have ever been evaluated in terms of augmentation programs for improved biocontrol. Parasites of the egg sacs include the flightless scelionid wasp Baeus latrodecti, and members of the chloropid fly genus Pseudogaurax. Predators of the adult spiders include a few wasps, most notably the blue mud dauber, Chalybion californicum, and the spider wasp Tastiotenia festiva. Other species including Mantis or Centipede also will occasionally and opportunistically take widows as prey, but the preceding all exhibit some significant specific preference for Latrodectus.
Although these spiders are not especially large, their venom is extremely potent. Compared to many other species of spiders, their chelicerae are not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1.0 millimeter (about 0.04 in) long, long enough to inject the venom to a point where it can be harmful. The males, being much smaller, inject far less venom with smaller chelicerae. The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of latrodectism). Deaths in healthy adults from Latrodectus bites are relatively rare in terms of the number of bites per thousand people. Sixty-three deaths were reported in the United States between 1950 and 1959. On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of this genus. Widow spiders have more potent venom than most spiders, and prior to the development of antivenom, 5% of reported bites resulted in fatalities. The venom can cause a swelling up to 15 cm. Improvements in plumbing have greatly reduced the incidence of bites and fatalities in areas where outdoor privies have been replaced by flush toilets.
There are a number of active components in the venom:
- A number of smaller polypeptides - toxins interacting with cation channels which display spatial structure homology - which can affect the functioning of calcium, sodium, or potassium channels.
The venom is neurotoxic.
- Fabricius, J. C. 1775. Systema entomologiae, sistens insectorum classes, ordines, genera, species, adiectis, synonymis, locis descriptionibus observationibus. Flensburg and Lipsiae, 832 pp. (Araneae, pp. 431-441). 
- Platnick, N. I.2008. The World Spider Catalog, version 9.0. American Museum of Natural History. 
- Kaston, B. J. (1970). "Comparative biology of American black widow spiders". Transactions of the San Diego Society of Natural History 16 (3): 33–82.
- Latrodectus hesperus. "Black Widow Spider, Black Widow Spider Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News - National Geographic". Animals.nationalgeographic.com. Retrieved 2009-02-18.
- "Southern black widow spider". Insects.tamu.edu. Retrieved 2009-03-10.
- "Widow Spiders". Ext.vt.edu. Retrieved 2009-02-18.
- Nevada's State Insects
- Marion H., Luis (1980-02-03). "Aracnoidismo en la Republica Dominicana". Medicina al Dia (in Spanish) (BVS). Retrieved 2012-10-08.
- Inirio, Juan Ramon (2009-11-06). "Detectan la peligrosa viuda negra". El Nacional (in Spanish). Retrieved 2012-10-08.
- Tenorio, Joanne M., and Gordon M. Nishida. 1995. What's Bugging Me? Identifying and Controlling Household Pests in Hawaii. University of Hawaii Press (Honolulu). 184+7 pp. illus. (publisher's listing)
- Scott, Susan, and Craig Thomas, M.D. 2000. Pest of Paradise: First Aid and Medical Treatment of Injuries from Hawaii's Animals. University of Hawaii Press (Honolulu). 190+xii pp. illus. (publisher's listing)
- Honolulu Star-Bulletin. 6 November 2008. Creepy critter caught in grapes.
- Import Health Standard Commodity Sub-class: Fresh Fruit/Vegetables Table grapes, (Vitis vinifera) from the United States of America--State of California (Issued pursuant to Section 22 of the (New Zealand) Biosecurity Act 1993; Date Issued: 18 August 2005).
- Jones, Susan C. (2000). Black Widow Spider Fact Sheet. Ohio State University, U.S.
- Breene, R . G . and M. H. Sweet (1985). "Evidence of insemination of multiple females by the male black widow spider, Latrodectus mactans (Araneae, Theridiidae)". The Journal of Arachnology 13 (3): 331–335.PDF
- Latrodetus Mactans McCorkle, Matthew. 17 October 2002.
- Foelix, R. (1982). Biology of Spiders, pp. 162-163. Harvard University, U.S.
- Miller T. Latrodectism: bite of the black widow spider. American Family Physician 1992; 45:181-187.
- Bettini S. Epidemiology of latrodectism. Toxicon 1964; 2:93-101.
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