Latrodectus mactans

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Geographic Range

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. (Comstock, 1948; Desert USA Magazine, 2004; Emerton, 1961; Milne and Milne, 1990; Shuttlesworth, 1959; Smith, 1980)

Habitat

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

Physical Description

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)

  • Sexual Dimorphism
  • female larger
  • Average mass
    1 g
    0.04 oz
  • Average length
    3-10 mm
    in

Development

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).

Reproduction

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

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.

Lifespan/Longevity

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

Behavior

Latrodectus mactans is timid, sedentary, solitary, cannibalistic, and nocturnal. The only social life it exhibits is when it mates. During the daylight hours, this spider spends its time in the silken tunnel of its web, which is the core of the snare. The female black widow spider hangs upside down in her web; her red hourglass marking is a visible warning signal. This spider will drop out of its web at the slightest disturbance and pretend that it is dead. The female black widow is usually clumsy when she is not in intimate contact with the lines of her snare. Latrodectus mactans is a tangled web weaver. Its irregular, funnel-shaped web of coarse silk has a definite plan. Three structural levels can be recognized: an uppermost complex of supporting threads, a central zone of tangle threads, and a lower zone of vertical trap threads. Also, the black widow spider is greatly active in the autumn months and its web is spread over everything. In addition, most of these spiders live only a year, but the yearly population is divided into two faunas, one identified with spring and the second with fall. (Ferrand, 1988; Shuttlesworth, 1959; Preston-Mafham, 1996; Hillyard, 1994; Gertsch, 1979; Kaston, 1953)

Food Habits

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)

Predation

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). (Desert USA Magazine, 2004; Farrand, 1988)

Ecosystem Roles

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

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. (Hillyard, 1994; Kaston, 1953; Preston-Mafham and Preston-Mafham, 1984; Shuttlesworth, 1959)

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. (Comstock, 1948; Gertsch, 1979; Hillyard, 1994; Kaston, 1953; Preston-Mafham and Preston-Mafham, 1996; Shuttlesworth, 1959)

  • Negative Impacts
  • injures humans

Conservation Status

Black widow spiders are fairly common and they are afforded no special conservation protections.

Other Comments

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). (Farrand, 1988; Kaston, 1953; Shuttlesworth, 1959)

Contributors

Matthew McCorkle (author), University of Michigan-Ann Arbor, Kerry Yurewicz (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

agricultural

living in landscapes dominated by human agriculture.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

References

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Desert USA Magazine, 2004. "Black Widow Spiders" (On-line). Accessed February 28, 2002 at http://www.desertusa.com/july97/du_bwindow.html.

Emerton, J. 1961. The Common Spiders of the United States. New York: Dover.

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Foelix, R. 1996. Biology of Spiders. New York: Oxford University Press.

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Lyon, W. "Black Widow Spider" (On-line). Accessed February 28, 2002 at http://ohioline.osu.edu/hyg-fact/2000/2061A.html.

Milne, L., M. Milne. 1990. The Audubon Society Field Guide to North American Insects. New York: Alfred A. Knopf, Inc..

National Integrated Pest Management Network North Carolina State University, "Black Widow Spider" (On-line). Accessed February 28, 2002 at http://ipm.ncsu.edu/AG369/notes/black_widow_spider.html.

Pechenik, J. 1991. Biology of the Invertebrates. Dubuque, Iowa: Wm. C. Brown.

Preston-Mafham, K., R. Preston-Mafham. 1984. Spiders of the World. New York: Blandford Press Ltd..

Preston-Mafham, K., R. Preston-Mafham. 1996. The Natural History of Spiders. Ramsbury, Marlborough: The Crowood Press Ltd..

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.

Snow, K. 1970. The Arachnids: An Introduction. New York: Columbia University Press.

Wallace, R., G. Sanders, R. Ferl. 1991. Biology, The Science of Life. New York: HarperCollins Publishers, Inc..