Widow Spider Envenomation

Updated: Sep 19, 2018
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Widow spiders belong to the genus Latrodectus and include the black widow spider (Latrodectus mactans mactans) in the United States. The term widow spider is used because not all species in the genus Latrodectus are black. Other widow spiders in North America include the brown widow (Latrodectus geometricus), the red-legged widow (Latrodectus bishopi), Latrodectus variolus, and Latrodectus hesperus. The redback spider (Latrodectus hasselti) is endemic to Australia. Latrodectus mactans tredecimguttatus and Latrodectus pallidus are found in Europe and South America, and the button spider (Latrodectus indistinctus) is found in South Africa.

The adult female black widow spider is approximately 2 cm in length and shiny black with a red-orange hourglass or spot on the ventral abdomen. The male is much smaller, brown, and incapable of envenomating humans. Juvenile females are also brown but have the general body morphology of the adult. Males and juveniles have a pale hourglass shape, similar to adult females. The female sometimes eats the male during or after copulation. Webs are irregular, low-lying, and commonly seen in garages, barns, outhouses, and foliage. Other widow spiders are generally black but may have red spots, such as Latrodectus mactans tredecimguttatus, or a dorsal red stripe, such as the redback spider. Latrodectus geometricus is brown with red and yellow markings.

See the images below.

Female black widow spider, Latrodectus mactans, in Female black widow spider, Latrodectus mactans, in the process of spinning her web on a tree branch. Note the characteristic red hourglass located on her inferior abdominal surface. This marking can vary in coloration from yellowish to shades of orange and red and, at times, white. The female’s body is an overall shiny jet-black in color. This spider was found on a farm in the US state of Georgia. By James Gathany (http://phil.cdc.gov/phil/) [Public domain], courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Black_widow_spider_9854_lores.jpg).
Female black widow spider guarding an egg case; sp Female black widow spider guarding an egg case; species Latrodectus mactans. By Chuck Evans (mcevan). [CC BY 2.5 (https://creativecommons.org/licenses/by/2.5)], courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Black_Widow_Spider_07-04-20.jpg).
Black widow spider (Latrodectus mactans) and offsp Black widow spider (Latrodectus mactans) and offspring. Photo by Sean Bush, MD.
A redback spider (Latrodectus hasseltii) female, f A redback spider (Latrodectus hasseltii) female, found in suburban Sydney, New South Wales, Australia. By Toby Hudson [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Latrodectus_hasseltii_close.jpg).
Young female Latrodectus tredecimguttatus; photo t Young female Latrodectus tredecimguttatus; photo taken in Croatia by K. Korlevic. No machine-readable author provided. Kork~commonswiki assumed (based on copyright claims). [Public domain], via Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Latrodectus_tredecimguttatus_female.jpg).

Envenomation is an uncommon occurrence with an extremely variable presentation. Treatment of envenomation often is based on speculation and anecdote, and much of the literature is contradictory. This article attempts to keep recommendations in agreement with the most current standards of care. This article serves as a guideline, and the clinician should use judgment for individual patient encounters.

See Arthropod Envenomation: From Benign Bites to Serious Stings and Venomous Spider Bites: Keys to Diagnosis and Treatment, Critical Images slideshows, for help identifying and treating various envenomations.



Alpha-latrotoxin causes the toxic effects observed in humans by opening cation channels (including calcium channels) presynaptically, causing increased release of multiple neurotransmitters. This results in excess stimulation of motor endplates with resultant clinical manifestations. Clinically, the predominant effects are neurological and autonomic, in contrast to the dermonecrotic local effects associated with spiders causing necrotic arachnidism (eg, brown spiders [Loxosceles species]).



According to the 2016 Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS), approximately 1300 widow spider bites were reported for 2016, [1] although this figure is probably conservative because of underreporting. No deaths caused by widow spider envenomation have been reported to the AAPCC since its first annual report in 1983. [1] Deaths after black widow spider bites were reported in 2001, [2] 2003, [3] and 2006 in Spain, Greece, and Albania (2 deaths), respectively. [4]



The vast majority of patients with widow spider envenomations recover fully.


Patient Education

For patient education resources, see the Bites and Stings Center, as well as Black Widow Spider Bite and Brown Recluse Spider Bite.