4Brown Widow Spider (Latrodectus geometricus)
The brown widow is thought to have evolved in Africa, but
the first specimen described came from South America. It is classified
as an invasive species elsewhere around the world. Brown widow
populations have appeared in southern California, the Caribbean, the
U.S. states of the Gulf Coast, as well as in Japan, South Africa and
Madagascar, Australia, and Cyprus. The species makes its home in
buildings, inside old tires, and under automobiles, as well as among
shrubs and other vegetation.
The spider has a brownish appearance that ranges from tan to almost black. The abdomens of some specimens have ornate dark-brown, black, white, yellow, or orange markings. Unlike other members of the genus, the hourglass marking on the underside of the brown widow is orange.
Brown widow venom is considered to be twice as powerful as that of the black widow; however, the species is not aggressive and only injects a tiny amount of venom when it bites. Still, brown widow bites were associated with the deaths of two people in Madagascar in the early 1990s. (These victims they were in poor health and they were not treated with antivenin.)
Latrodectus geometricus, commonly known as the brown widow,[1][2] grey widow, brown black widow,[2] house button spider or geometric button spider, is one of the widow spiders in the genus Latrodectus. As such, it is a 'cousin' to the more infamous Latrodectus mactans (black widow).
Brown widows can be located by finding their egg sacs, which are easily identifiable. They resemble a sandspur, having pointed projections all over,[4] and they are sometimes described as "tufted", "fluffy",[4] or "spiky" in appearance. Eggs hatch in approximately 20 days.[7] Female brown widows "lay about 120-150 eggs per sac and can make 20 egg sacs over a lifetime."[1]
Like all Latrodectus species, L. geometricus has a neurotoxic venom that, drop for drop, is as toxic as the black widow's. However, brown widow bites are usually not very dangerous; usually much less dangerous than the black widow's.[3] The effects of the toxin are usually confined to the bite area and surrounding tissue, unlike the black widow's.[4] 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.[1] The LD-50 of L. geometricus venom has been measured in mice as 0.43 mg/kg.,[8] and separately again as 0.43 mg/kg (with a confidence interval of 0.31-0.53).[9]
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. Brown button spiders are known to have a lifespan of about two years.[10]
The spider has a brownish appearance that ranges from tan to almost black. The abdomens of some specimens have ornate dark-brown, black, white, yellow, or orange markings. Unlike other members of the genus, the hourglass marking on the underside of the brown widow is orange.
Brown widow venom is considered to be twice as powerful as that of the black widow; however, the species is not aggressive and only injects a tiny amount of venom when it bites. Still, brown widow bites were associated with the deaths of two people in Madagascar in the early 1990s. (These victims they were in poor health and they were not treated with antivenin.)
Geographic distribution
The brown widow is thought by some researchers to originate in South Africa.[2] The origin of this species is uncertain, as specimens were discovered in both Africa and South America.[1] They are usually found around buildings in tropical areas. They can compete with populations of the black widow spider.[3] It has migrated to many parts of the world. It is found in many areas of the United States,[1][2][4][4] Australia,[1] Afghanistan, China, Japan,[5] Tanzania,[citation needed] Dominican Republic,[6] Cyprus,[1] Costa Rica, El Salvador, and Brazil, and there have been sightings in the United Arab Emirates and Thailand.Description
L. geometricus is slightly smaller[4] 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. Although the Latin name comes from this pattern, a spider's coloring can and does darken over time and the pattern may become obscured. Also, they have stripes on their legs. Brown widows are often preyed on by mud daubers and sometimes by digger wasps.
A brown widow's egg sac
Like all Latrodectus species, L. geometricus has a neurotoxic venom that, drop for drop, is as toxic as the black widow's. However, brown widow bites are usually not very dangerous; usually much less dangerous than the black widow's.[3] The effects of the toxin are usually confined to the bite area and surrounding tissue, unlike the black widow's.[4] 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.[1] The LD-50 of L. geometricus venom has been measured in mice as 0.43 mg/kg.,[8] and separately again as 0.43 mg/kg (with a confidence interval of 0.31-0.53).[9]
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. Brown button spiders are known to have a lifespan of about two years.[10]
References
- Vetter, Richard S. (2013). "The brown widow spider, Latrodectus geometricus". Department of Entomology, Center for Invasive Species Research, University of California, Riverside. Retrieved 15 July 2013.
- Reagan, Mark (12 August 2011). "It's officially confirmed: There's a new spider in southwest Kansas". Dodge City Daily Globe. Retrieved 28 September 2012.
- Brown, Eryn (2 July 2012). "Brown widow spiders 'taking over' in Southern California". Science Now (Los Angeles Times). Retrieved 28 September 2012.
- Santana, Fred (2007). "Brown Widow Spiders". Sarasota County, Florida: Institute of Food and Agricultural Sciences, University of Florida. Retrieved 28 September 2012.
- Ono, H (1995). "Records of Latrodectus geometricus (Araneae: Theridiidae) from Japan". Acta Arachnologica 44 (2): 167–170. doi:10.2476/asjaa.44.167.
- "Hallan araña Viuda Marrón en Salinas de Baní" (in Spanish). El Nacional. 24 January 2012. Retrieved 8 October 2012.
- Jackman, J A (2006). "Spiders", Texas Agricultural Extension Service.
- Rauber, Albert (1 January 1983). "Black Widow Spider Bites". Clinical Toxicology 21 (4-5): 473–485. doi:10.3109/15563658308990435. PMID 6381753.
- McCrone, J.D. (1 December 1964). "Comparative lethality of several Latrodectus venoms". Toxicon 2 (3): 201–203. doi:10.1016/0041-0101(64)90023-6.
- Murphy, Chris (4 March 2012). "Welcome to your nightmares: Meet the spider so tough it eats SNAKES for breakfast". Daily Mail. Retrieved 28 September 2012.
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