Latrodectus mactans goes by several names. It received the name “widow” because females sometimes kill and eats their mates after mating has taken place. However, the sexes can separate peaceably and the male may even mate again (Farrand, 1988; Kaston, 1953). Other names that are associated with the black widow spider are “the hourglass spider” because of the red hourglass shaped mark on the female’s abdomen or “the shoe button spider” due to the form of the spider’s jet-black abdomen (Shuttlesworth, 1959).
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
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).
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 )
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
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
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)
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 )
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
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.
Average lifespan
Status: wild: 3 years.
Range lifespan
Status: captivity: 4 (high) hours.
Average lifespan
Status: wild: 1 years.
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 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).
Known Predators:
Anti-predator Adaptations: aposematic
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 ; gonochoric/gonochoristic/dioecious (sexes separate); 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
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)
Latrodectus mactans, known as southern black widow or simply black widow, and the shoe-button spider, is a venomous species of spider in the genus Latrodectus. The females are well known for their distinctive black and red coloring and for the fact that they will occasionally eat their mates after reproduction. The species is native to North America. The venom can cause pain and other symptoms, but is rarely fatal to healthy humans.[2]
Latrodectus mactans was first described by Johan Christian Fabricius in 1775, placing it in the genus Aranea.[1][3] It was transferred to the genus Latrodectus in 1837 by Charles Walckenaer and is currently placed in the family Theridiidae of the order Araneae.[1] 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,[4] 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 body length (excluding legs) of the mature female is 8–13 mm (0.31–0.51 in), and 3–6 mm (0.12–0.24 in) for males. Legs are long in proportion to body.[5] Females are 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.[6] There is much variation in female size, particularly in egg-carrying (gravid) females. The abdomen of a gravid female can be more than 1.25 cm (0.5 in) in diameter. Many female widows also have an orange or red patch just above the spinnerets on the top of the abdomen.[7] Juveniles have a distinctly different appearance from the adults; the abdomen is grayish to black with white stripes running across it and is spotted with yellow and orange.[7] Males are either purple, or closer to the appearance of the juveniles in color.
The web of the black widow spider is a three-dimensional tangled cobweb of exceptionally strong silk.[8]
The southern widow is primarily found in (and is indigenous to) the southeastern United States, ranging as far north as Ohio and as far west as Texas.[9] The northern black widow (L. variolus) is found primarily in the northeastern United States, though its range overlaps with that of L. mactans. In the Dominican Republic L. mactans is found throughout the whole country.[10][11] L. mactans is also found throughout Mexico where its range overlaps with that of Latrodectus hesperus and Latrodectus geometricus.[12]
L. mactans, along with L. hesperus and L. geometricus, is established in the Hawaiian Islands (USA).[13][14] One pathway of entry into Hawaii for at least one of these black widow species is imported produce[15] (which is also considered an important potential pathway for widow spiders elsewhere).[16]
When a male is mature, he spins a sperm web, deposits semen on it, and charges his palpal bulbs with the sperm. Black widow spiders reproduce sexually when the male inserts his palpal bulbs 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 due to cannibalism, lack of food, and/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 three years, while a male's lifespan is about three to four months.[17] The female may eat the male after mating.
Black widow spiders typically prey on a variety of insects, with a preference for fire ants if extant, but they also feed on woodlice, diplopods, and chilopods when they are young, and occasionally other arachnids. [18] The spider's web is even strong enough to catch animals as large as mice. 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.[19]
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,[20] and members of the chloropid fly genus Pseudogaurax. Predators of the adult spiders include the brown widow spider, Latrodectus geometricus,[21] wasps, most notably the blue mud dauber Chalybion californicum, and the spider wasp Tastiotenia festiva. Other organisms including mantises or centipedes also will occasionally and opportunistically take widows as prey, but the preceding all exhibit some significant specific preference for Latrodectus.
The brown widow appears to be competing for territory with, and ultimately displacing black widows in areas where they occur together, including predation on black widows.[21][22]
Although the reputation of these spiders is notorious and their venom does affect humans, only mature females are capable of envenomation in humans; their chelicerae—the hollow, needle-like mouthparts that inject venom—are approximately 1 mm, or .04 in. in length, making them long enough to inject venom into humans, unlike those of the much smaller males. The actual amount injected, even by a mature female, is variable. The venom injected by the female black widow is known as alpha-latrotoxin which binds to receptors at the neuromuscular motor end plate of both sympathetic and parasympathetic nerves, resulting in increased synaptic concentration of catecholamines. The symptoms are caused by lymphatic absorption and vascular dissemination of the neurotoxin. The symptoms that result from a black widow spider bite are collectively known as latrodectism. Deaths in healthy adults from Latrodectus bites are exceedingly rare, with no deaths despite two thousand bites yearly, and studies within the past several decades have been unable to confirm any fatalities from this or any of the other U.S. species of Latrodectus (e.g. zero fatalities among 23,409 documented Latrodectus bites from 2000 through 2008).[23] On the other hand, the geographical range of the widow spiders is vast. Epidemics of mostly European widow spider bites had been recorded from 1850 to 1950, and during that period deaths were reported from 2 per 1000 bites to 50 per 1000 bites. Deaths from the western black widow had been reported as 50 per 1000 bites in the 1920s. At that same time, antivenom was introduced.[24] The LD-50 of L. mactans venom has been measured in mice as 1.39 mg/kg,[25] and separately as 1.30 mg/kg (with a confidence interval of 1.20–2.70).[26] In 1933, Allan Blair allowed himself to be bitten by the spider in order to investigate the toxicity of its venom in humans and as a means of convincing skeptics at the time who thought that the spider's venom might not be dangerous to humans.
There are a number of active components in the venom:
The venom is neurotoxic.
Latrodectus mactans, known as southern black widow or simply black widow, and the shoe-button spider, is a venomous species of spider in the genus Latrodectus. The females are well known for their distinctive black and red coloring and for the fact that they will occasionally eat their mates after reproduction. The species is native to North America. The venom can cause pain and other symptoms, but is rarely fatal to healthy humans.
