Black widow spider (Latrodectus mactans)

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Black widow female showing distinctive red egg-timer shaped markings on abdomen

Top facts

  • Contrary to popular belief, the female black widow spider does not always eat the male after mating.
  • The black widow spider is extremely poisonous, although an effective anti-venom is available.
  • The female black widow spider can be twice as big as the male and has a characteristic red hourglass marking on the underside of its body.
  • Young black widow spiders go though multiple moults before gaining a similar appearance to the adults.
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Black widow spider fact file

Black widow spider description

KingdomAnimalia
PhylumArthropoda
ClassArachnida
OrderAraneae
FamilyTheridiidae
GenusLatrodectus (1)

The black widow spider (Latrodectus mactans) is a sexually dimorphic spider, with the female being almost twice as big as the male and rather different in pattern and colouration (3). This species gains its common name from the common misconception that the female regularly eats the male after mating (3) (4).

The female black widow spider has a shiny black body and legs (2) (3) (4) and the underside of the body features a characteristic red hourglass-like marking (2) (3) (4), which can appear yellow or orange in certain individuals (3).

The male is also black, with a narrower abdomen than the female, and may have white lines running along the sides of its body and red spots along the centre of the upperside (2) (3) (4). It has a smaller body than the female and longer legs (3), which may have lightly coloured rings along them from earlier moults (4).

The young black widow spider is orange, yellow-white or white and gradually gains the black colouration of the adult as it ages and undergoes a series of moults (2) (3). It may also have the white stripes along the side of the body which are seen in the adult male (2).

Although there are no recognised subspecies of black widow spider, there is much variation in colour and size between southern and western populations (2)

Size
Female body length: c. 9 mm (2)
Male body length: c. 4 mm (2)
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Black widow spider biology

The breeding season of the black widow spider occurs between late spring and early autumn (4), with the female laying eggs into several pear-shaped egg sacs, which are white, tan or grey and have a paper-like texture (2) (3) (4). These sacs can contain up to 400 eggs and are suspended within the web, with the female keeping guard nearby (2) (3).

About four weeks after the eggs have been laid, the eggs hatch and the spiderlings emerge from the sac (2) (3), after performing their first moult (3). In order to disperse effectively, the spiderlings release silk threads, which enable them to be carried in the wind (3). Several moults are performed before the young reach maturity (3) (4).

The black widow spider feeds on a wide variety of arthropods, which are caught using the web as a trap (2) (3) (4). Young black widow spiders can become highly cannibalistic from ten days after hatching (2).

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Black widow spider range

The black widow spider is mostly found in the southeast United States, although it is known to occur as far north as New York (4).

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Black widow spider habitat

The black widow spider builds webs close to the ground in dark sheltered areas, both outdoors under wood piles, stones and in the hollow stumps of dead trees, and in indoor areas such as outbuildings, basements and barns (2) (3).

Within the web, this spider commonly builds a retreat where it spends most of its time, only leaving when prey becomes caught in the web or to repair damage to it (2).

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Black widow spider status

The black widow spider has yet to be classified by the IUCN.

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Black widow spider threats

There are not currently thought to be any major threats to the black widow spider.

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Black widow spider conservation

There are not known to be any specific conservation measures currently in place for the black widow spider.

View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

Find out more about the black widow spider:

  • Kaston, B.J. (1972) Comparative biology of American black widow spiders. Transactions of the San Diego Society of Natural History,16: 33-82.
  • Ohio State University Extension Factsheet - Black widow spider (August, 2012)
    http://ohioline.osu.edu/hyg-fact/2000/pdf/2061A.pdf
  •  
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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Abdomen
In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders).
Arthropods
A major grouping of animals that includes crustaceans, insects and arachnids. All arthropods have paired jointed limbs and a hard external skeleton (exoskeleton).
Moult
In insects, a stage of growth whereby the hard outer layer of the body (the exoskeleton) is shed and the body becomes larger.
Sexual dimorphism
When males and females of the same species differ in appearance.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
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References

  1. UNEP-WCMC (August, 2012)
    http://www.unep-wcmc.org/
  2. Texas A&M University: Department of Entomology - Southern black widow spider (August, 2012)
    http://insects.tamu.edu/fieldguide/cimg368.html
  3. Ohio State University Extension Factsheet - Black widow spider (August, 2012)
    http://ohioline.osu.edu/hyg-fact/2000/pdf/2061A.pdf
  4. Kaston, B.J. (1972) Comparative biology of American black widow spiders. Transactions of the San Diego Society of Natural History,16: 33-82.
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Image credit

Black widow female showing distinctive red egg-timer shaped markings on abdomen  
Black widow female showing distinctive red egg-timer shaped markings on abdomen

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