Latrodectus geometricus

Brown Widow

Synonym(s):  
Class: Arachnida
Order: Araneae
Family: Theridiidae


Photographer: Richard S. Vetter
Source: http://cisr.ucr.edu/brown_widow_spider.html

Description

Adult Description: The brown widow spider (Latrodectus geometricus) can vary in color from white, dark brown, to almost black, however most are light or medium brown. The ventral side of the abdomen contains an orange or yellow colored hour glass shaped marking, brown shaded bands on leg segments, white spots on the abdomen, and white stripes marginally. The white abdominal stripes can distinguish this species from the black widow, but the white stripes are often difficult to see on darker colored brown widow spiders. The body size differs by gender; the female body length is typically 12-16mm (not including legs), while the male's length is 6-8mm, but with longer legs compared to that of the female.

Larva Description: The female brown widow spider carries a tan, spherical egg sac (20-30 day incubation period) beneath her abdomen producing offspring that looks like smaller versions of the adult. The brown widow spider reaches maturation after 4 months, but the male undergoes fewer molts to reach maturation.

Host Plant: None

Ecological Threat: Currently, the brown widow spider does not pose the same medical concerns as the black widow spider. Bites from the brown widow do not cause the same symptoms as the black widow. Brown widow spider venom is twice as potent as black widow venom, it is believed the brown widow does not inject the same amount of neurotoxin. This, results in the decreased severity of symptoms in the form of cramping or nausea. This species is timid avoids human interaction. In fact, males and immature brown widow spiders do not bite at all. This species will fall to the ground in a ball as if it were dead as a defense mechanism, but should not be handled. Brown widow spiders bite out of defense, and it will only occur by mature females.

Biology: Female brown widow spiders have a relatively long life span with the possibility of living up to 3 years, while the male brown widow life span is only 6 months to 1 year. The brown widow is a rapidly reproducing spider with females producing up to 5,000 young each season. Due to its ability to reproduce rapidly the brown widow is difficult to control or eliminate.

History: The brown widow spider originated in South Africa and was transferred to the U.S. through Florida. The spider is believed to have become established in the U.S. by attaching to the bottom of vehicles and being transported to other locations.

U.S. Habitat: The brown widow spider prefers tropical climates, and is commonly found in the southeast United States where it was introduced. This spider can be found on many man-made structures in dark corners or crevices around houses, barns, fences, or anywhere a web will fit near the ground. The web contains a retreat structure or tunnel to allow the spider to hide or escape from predators. The Brown Widow spider feeds on insects, and is known to kill anything that gets tangled in its web.

Distribution

Native Origin: South Africa

U.S. Present: FL, GA, SC, MS, AL, CA, AR, CO, and TX

Resembles/Alternatives

The Brown Widow spider resembles the Black Widow spider (Latrodectus mactans), but can be most readily distinguished if an egg sac is present. The Brown Widow spider egg sac is tan with many tufts of silk protruding from the ovular shape resembling a thistle. The Black Widow spider produces egg sacs that are white and pear shape with a smooth exterior and no protrusions.

Management

Routine cleaning is the most effective way to prevent the brown widow spider from becoming established. Reducing clutter, sealing cracks, and vacuuming regularly makes areas less appealing. When vacuuming a suspected infestation it is important to empty the vacuum bag and seal in a plastic bag before disposing it. Ensuring wood or leaf litter piles are removed or not near homes and barns also helps prevent the Brown Widow from entering structures.

Sanitation is the best natural defense to the brown widow. However, if this approach does not help or there are areas where vacuuming is not possible insecticides may be used in the form of aerosol spray and insect powder. Aerosol sprays are effective on colonies that have living spiders and prevents their reestablishment. Insect dusts are effective as well because the dust clings to the spider's web which effectively poisons the spider when it eats the web to recycle the material.

Perimeter or topical sprays are not effective long term because the sun reduces the effectiveness over short periods of time. These types of sprays also cause unsafe pesticide contact with humans and pets.

SEARCH Online

Google Search: Latrodectus geometricus
Google Images: Latrodectus geometricus
NatureServe Explorer: Latrodectus geometricus
Bugwood Network Images: Latrodectus geometricus

References

Benjamin, Suresh P., Samuel Zschokke. 2003. Webs of theridiid spiders: construction, structure and evolution. Biological Journal of the Linnean Society 78(3): 293-305.

Brown, K. S., J. S. Necaise, J. Goddard. 2008. Additions to the Known U.S. Distribution of Latrodectus geometricus (Araneae: Theridiidae). Journal of Medical Entomology 45(5): 959-962.

Hedges, Stoy, Mark S. Lacey. 1995. Field Guide for the Management of Urban Spiders-PCT Pest Control Technology. Franzak and Foster Company, Cleveland.

Sampayo, Rafael R. 1944. Pharmacoloical action of the venom of Latrodectus mactans and other Latrodectus spiders. The Journal of Pharmacology and Experimental Therapeutics 80(4): 309-322.

Internet Sources

http://bugguide.net
http://sarasota.ifas.ufl.edu/ipm

 

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