Latrodectus geometricus

L. geometricus derives its name from the geometric patterning on its abdomen. However, the spider's coloring can and does darken over time and the pattern may become obscured.

Similar widows include the L. rhodesiensis, a brown-colored relative of L. geometricus which is native to Zimbabwe. Both species are collectively known as brown button spiders throughout southern Africa.

L. geometricus is slightly smaller and generally lighter in color than the black widow species; the color can range from tan to dark brown to black, with shades of grey also possible. Like the black widow species in the United States, L. geometricus has a prominent hourglass-shaped marking on the underside of the abdomen; the brown widow's hourglass, however, is usually a vivid orange or a yellowish color. Unlike the black widow, L. geometricus has a black-and-white geometric pattern on the dorsal side of its abdomen. They also have stripes on their legs.

Brown widows can be located by finding their egg sacs, which are easily identifiable. They resemble a sandspur, having pointed projections all over, and they are sometimes described as "tufted", "fluffy", or "spiky" in appearance. Eggs hatch in approximately 20 days.Jackman, J A (2006). "[http://ward-co.tamu.edu/publications/spi.pdf Spiders] {{webarchive|url=https://web.archive.org/web/20070822052011/http://ward-co.tamu.edu/publications/spi.pdf |date=22 August 2007 }}", Texas Agricultural Extension Service. Female brown widows lay about 120–150 eggs per sac and can make 20 egg sacs over a lifetime.

Because L. geometricus is dispersed all around the globe, they have many predators. Brown widows are commonly preyed upon by different types of wasps, including mud daubers and digger wasps.

The brown widow has a cosmopolitan distribution. The World Spider Catalog gives its native distribution as Africa, with introductions to the Americas, Poland, the Middle East, Pakistan, India, Thailand, Japan, China, Papua New Guinea, Australia and Hawaii. It is thought by some researchers to originate in South Africa, although this is uncertain, as specimens were discovered in both Africa and South America.{{cite web | url= http://cisr.ucr.edu/brown_widow_spider.html |title= The brown widow spider, Latrodectus geometricus | first= Richard S. | last= Vetter | publisher= Department of Entomology, Center for Invasive Species Research, University of California, Riverside | year=2013 | accessdate= 15 July 2013}} They are usually found around buildings in tropical areas. They can compete with populations of the black widow spider. It is found in many areas of South Africa, the United States (including Hawaii),{{cite web | url= http://sarasota.ifas.ufl.edu/IPM/BrownWidow.htm | title= Brown Widow Spiders | first= Fred | last= Santana |publisher= Institute of Food and Agricultural Sciences, University of Florida | location= Sarasota County, Florida | year= 2007 | accessdate= 28 September 2012}} Australia, Japan,{{cite journal | last= Ono | first= H | year= 1995 | title= Records of Latrodectus geometricus (Araneae: Theridiidae) from Japan | journal= Acta Arachnologica | volume= 44 | pages= 167–170 | issue= 2 | doi= 10.2476/asjaa.44.167 | doi-access= free }} the Dominican Republic,{{cite web | url=http://elnacional.com.do/hallan-arana-viuda-marron-en-salinas-de-bani| title=Hallan araña Viuda Marrón en Salinas de Baní| language=Spanish |publisher=El Nacional | date= 24 January 2012 | accessdate= 8 October 2012}} Costa Rica,{{cite journal | url=https://www.scielo.sa.cr/scielo.php?script=sci_arttext&pid=S0001-60022017000200073| title=Latrodectism in Costa Rica| journal=Acta Médica Costarricense| language=Spanish |publisher=SciCielo Costa Rica | date= June 2017 | volume=59| issue=2| pages=73–74| accessdate= 11 November 2024| last1=Barrantes-Montero| first1=Gilbert| last2=Valerio-Pizarro| first2=Raquel| last3=Barrantes-Montero| first3=Gilbert| last4=Valerio-Pizarro| first4=Raquel}} and Cyprus.

As of 2012, researchers at the University of California, Riverside, suggested that the brown widow spider, newly established in Southern California, may in fact be displacing black widow spiders from the region, competing and/or fighting for territory.Are Brown Widow Spiders Displacing Black Widows? http://www.entsoc.org/press-releases/are-brown-widow-spiders-displacing-black-widows{{Cite journal |last1=Vetter |first1=Richard S. |last2=Vincent |first2=Leonard S. |last3=Danielsen |first3=Douglas W.R. |last4=Reinker |first4=Kathryn I. |last5=Clarke |first5=Daniel E. |date=July 2012 |title=The Prevalence of Brown Widow And Black Widow Spiders in Urban Southern California |pmid=22897057 |journal=Journal of Medical Entomology |doi=10.1603/me11285 |volume=49 |issue=4 |pages=947–51|doi-access=free }} While certainly not definitive, this evidence does suggest that the brown widow is likely to be more hostile and aggressive towards its relative, the black widow, than the black widow is towards it. If that proves to be true, humans may be positively affected since brown widow bites are less toxic than those of black widows, thus posing less of a threat as they displace black widows over time.

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Like all Latrodectus species, L. geometricus has a neurotoxic venom. The venom acts on nerve endings causing the very unpleasant symptoms of latrodectism. However, brown widow bites are usually not very dangerous; usually much less dangerous than those of L. mactans, the black widow.{{cite news| url=https://www.latimes.com/science/la-xpm-2012-jul-02-la-sci-sn-brown-widow-spider-california-20120702-story.html | title= Brown widow spiders 'taking over' in Southern California | first= Eryn | last= Brown | work= Los Angeles Times | date= 2 July 2012 | access-date= 28 September 2012}} The effects of the toxin are usually confined to the bite area and surrounding tissue, unlike the black widow's. Mere toxicity of the venom is not the only factor in dangerousness. Brown widow bites are minor compared to black widow bites because they cannot deliver the same amount of venom as the black widow. The LD₅₀ of L. geometricus venom has been measured in mice as 0.43 mg/kg,{{cite journal|last=Rauber|first=Albert|title=Black Widow Spider Bites|journal=Clinical Toxicology|date=1 January 1983|volume=21|issue=4–5|pages=473–485|doi=10.3109/15563658308990435|pmid=6381753}}{{cite journal|last=McCrone|first=J.D.|title=Comparative lethality of several Latrodectus venoms|journal=Toxicon|date=1 December 1964|volume=2|issue=3|pages=201–203|doi=10.1016/0041-0101(64)90023-6|pmid=14298228|bibcode=1964Txcn....2..201M }}

{{Reflist|refs=

{{citation |mode=cs1 |title=Taxon details Latrodectus geometricus C.L. Koch, 1841 |work=World Spider Catalog |publisher=Natural History Museum Bern |url=http://www.wsc.nmbe.ch/species/39047 |accessdate=2016-10-29 }}

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• [https://archive.today/20121007171615/http://www3.interscience.wiley.com/journal/119400198/abstract Sexual Cannibalism in the Brown Widow Spider (Latrodectus geometricus)]
• [http://cisr.ucr.edu/brown_widow_spider.html Brown Widow Spider at the Center for Invasive Species Research]
• {{Cite web |title=Brown widow spider - Latrodectus geometricus |url=https://entnemdept.ufl.edu/creatures/URBAN/SPIDERS/brown_widow_spider.htm |access-date=2023-03-15 |website=entnemdept.ufl.edu |last1=Hall |first1=Donald W. |date=February 2016 |series=Featured Creatures |publisher=Entomology and Nematology Department, University of Florida}}

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geometricus

Category:Cosmopolitan spiders

Category:Spiders described in 1841

Category:Taxa named by Carl Ludwig Koch