Latrodectus geometricus

Habitat and ecology

Latrodectus geometricus 300943521 542268330.jpg|female with egg sac Latrodectus geometricus 300943521 542268842.jpg| Latrodectus geometricus 305447352 550735451.jpg|dark female This species constructs three-dimensional webs in dark corners in a variety of microhabitats and is commonly found around houses. The egg sac is distinctive with spikes.

L. geometricus builds webs with a retreat from which delaying retreats radiate. From the delaying threads to the ground, sticky threads are laid down. The retreat has either one or two openings, with the main one opening onto the delaying threads. Webs are built at varying heights above the ground in vegetation and around buildings.

In South Africa, Latrodectus geometricus inhabits a large range at altitudes from 0 to 1941 m above sea level. It has been sampled from all floral biomes in South Africa and is commonly found in crops including avocado, citrus, cotton, maize, pistachio, prickly pears, and vineyards.

Geographic distribution

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. 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), Australia, Japan, the Dominican Republic, Costa Rica, and Cyprus.

Threat to native species

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. 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.

Description

Brown widow spider Latrodectus geometricus underside.jpg|Orange hourglass marking Latrodectus RUSVM egg sac.jpg|egg sac 20140627 001020CLOSE.jpg|Cairo, Egypt ViudaCafé_variación_oscura.png|dark color variation Costa Rica

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. Female brown widows lay about 120–150 eggs per sac and can make 20 egg sacs over a lifetime.

Taxonomy

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.

Predators

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.

Toxicology

Main article: Latrodectism

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. 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,

Conservation

Latrodectus geometricus is listed as Least Concern by the South African National Biodiversity Institute due to its wide geographical range. The species is well protected in more than ten reserves and parks.

Taxonomy

The species was revised by Lotz in 1994.

References

References

1. "Latrodectus geometricus C. L. Koch, 1841". World Spider Catalog.
2. (July 2012). "The Prevalence of Brown Widow And Black Widow Spiders in Urban Southern California". Journal of Medical Entomology.
3. (2021). "The Theridiidae of South Africa. Part 1 A-P". South African National Survey of Arachnida Photo Identification Guide.
4. Reagan, Mark. (12 August 2011). "It's officially confirmed: There's a new spider in southwest Kansas". [[Dodge City Daily Globe]].
5. Jackman, J A (2006). "[http://ward-co.tamu.edu/publications/spi.pdf Spiders] {{webarchive. link. (22 August 2007 ", Texas Agricultural Extension Service.)
6. Ono, H. (1995). "Records of Latrodectus geometricus (Araneae: Theridiidae) from Japan". Acta Arachnologica.
7. (24 January 2012). "Hallan araña Viuda Marrón en Salinas de Baní". El Nacional.
8. (June 2017). "Latrodectism in Costa Rica". SciCielo Costa Rica.
9. Are Brown Widow Spiders Displacing Black Widows? http://www.entsoc.org/press-releases/are-brown-widow-spiders-displacing-black-widows {{Webarchive. link. (22 December 2015)
10. Rauber, Albert. (1 January 1983). "Black Widow Spider Bites". Clinical Toxicology.
11. McCrone, J.D.. (1 December 1964). "Comparative lethality of several Latrodectus venoms". Toxicon.
12. Koch, C.L.. (1841). "Die Arachniden. Achter Band". C. H. Zeh'sche Buchhandlung.
13. Lotz, L.N.. (1994). "Revision of the genus Latrodectus (Araneae: Theridiidae) in Africa". Navorsinge van die Nasionale Museum Bloemfontein.
14. Santana, Fred. (2007). "Brown Widow Spiders". Institute of Food and Agricultural Sciences, University of Florida.
15. Brown, Eryn. (2 July 2012). "Brown widow spiders 'taking over' in Southern California". [[Los Angeles Times]].
16. Vetter. (2013). "The brown widow spider, ''Latrodectus geometricus''". Department of Entomology, Center for Invasive Species Research, [[University of California, Riverside]].