Medscape is available in 5 Language Editions – Choose your Edition here.


Redback Spider Envenomation

  • Author: Nathan Reisman, MD; Chief Editor: Joe Alcock, MD, MS  more...
Updated: Aug 24, 2015


The redback spider (Latrodectus hasselti) belongs to the family Theridiidae, the comb-footed spiders. Its genus Latrodectus also includes black widows, whose name may be more familiar to North American readers. The redback spider can be found throughout Australia, although it is more commonly seen in the temperate regions than in the colder, southern areas. The spider exists in higher numbers in Australia's urban and suburban areas and is virtually absent in the continent's forests. Outside of Australia, similar species of Latrodectus include Karakurt in Central Asia, Malmignatte in Europe, the Koppie spider in South Africa, and the Night Stinger in New Zealand.

The redback spider bite is the most common envenomation treated with antivenom in Australia. The female redback spider is responsible for most envenomations. She is usually 10 mm in length and has a small cephalothorax and a large, globular abdomen that bears a red, orange, or brown stripe. The male redback spider is considerably smaller than the female and is only occasionally able to cause mild envenomation.[1, 2] See the images below.

Female redback spider showing a distinctive red st Female redback spider showing a distinctive red stripe over the abdomen. Image courtesy of John Paterson.
Female redback spider with egg sacs. Image courtes Female redback spider with egg sacs. Image courtesy of John Paterson.

See Venomous Spider Bites: Keys to Diagnosis and Treatment, a Critical Images slideshow, for help identifying and treating various envenomations.



The redback spider can cause a clinical condition referred to as latrodectism following a bite. The active ingredient in the redback's venom responsible for its toxic properties in vertebrates is a 130-kd protein, alpha-latrotoxin (aLTX). aLTX is a potent neurotoxin that works in 2 ways to produce efflux of neurotoxins from presynaptic nerve cells.

In one mechanism of action, aLTX aggregates into tetramers that form pores in neuronal presynaptic cell membranes allowing calcium influx into the cytosol and resulting in exocytosis of neurotransmitters such as norepinephrine, dopamine, acetylcholine, glutamate, and GABA. The membrane pores formed by aLTX may also be large enough for a direct efflux of small intracellular compounds that are vital for cytoplasm function.

The monomeric aLTX can also act by activating latrophilin (LPH), an aLTX receptor found on the cell surface of neuronal cells, without incorporating into the cell membrane. Latrophilin is a G protein-coupled receptor that activates phospholipase C, which, in turn, increases the cytosolic concentration of IP3 leading to release of calcium from intracellular stores. This rise in cytosolic calcium increases the rate of spontaneous exocytosis of neurotransmitters and the amplitude of evoked release. Alpha-latrotoxin is a potent venom, with an LD-50 of 20-40 µg/kg of body weight in mice.[3, 4, 5]




United States

Only the black widow spider, a close relative of the redback spider, lives in the United States. These arachnids cause approximately 2500 envenomations each year.


The redback spider is found in Australia, New Zealand, and southern Asia. In Australia, the spider has been blamed for 250 envenomations requiring antivenom annually. Perhaps many more cases are mild or unrecognized and do not receive antivenom.


All races are susceptible to redback spider envenomation if the patient lives in an endemic area inhabited by the redback spider. One article shows more severe envenomation in Aboriginal patients, but states that this is due to a significantly longer time from envenomation to presentation in ED as compared with non-Aboriginal patients.[6]


In one study of redback envenomations in Australia, 60% of victims were female. However, most sources do not demonstrate a male/female sex discrepancy.[7]


Redback envenomation may occur at any age; the median age is 35 years. Envenomation may be more dangerous in babies and small children because of the difficulty in making a specific diagnosis in that group of patients in addition to the small body size bearing the same dose of injected poison as an adult would tolerate.[7]

Contributor Information and Disclosures

Nathan Reisman, MD Clinical Assistant Instructor, Department of Emergency Medicine, Kings County Hospital Center, SUNY Downstate Medical Center

Nathan Reisman, MD is a member of the following medical societies: Emergency Medicine Residents' Association, Society for Simulation in Healthcare

Disclosure: Nothing to disclose.


Sage W Wiener, MD Assistant Professor, Department of Emergency Medicine, State University of New York Downstate Medical Center; Director of Medical Toxicology, Department of Emergency Medicine, Kings County Hospital Center

Sage W Wiener, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Medical Toxicology, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

John T VanDeVoort, PharmD Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals

John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists

Disclosure: Nothing to disclose.

Matthew M Rice, MD, JD, FACEP Senior Vice President, Chief Medical Officer, Northwest Emergency Physicians of TeamHealth; Assistant Clinical Professor of Medicine, University of Washington School of Medicine Pending Approval

Matthew M Rice, MD, JD, FACEP is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, National Association of EMS Physicians, Society for Academic Emergency Medicine, Washington State Medical Association

Disclosure: Nothing to disclose.

Chief Editor

Joe Alcock, MD, MS Associate Professor, Department of Emergency Medicine, University of New Mexico Health Sciences Center

Joe Alcock, MD, MS is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Robert L Norris, MD Professor, Department of Emergency Medicine, Stanford University Medical Center

Robert L Norris, MD is a member of the following medical societies: American College of Emergency Physicians, Society for Academic Emergency Medicine, International Society of Toxinology, American Medical Association, California Medical Association, Wilderness Medical Society

Disclosure: Nothing to disclose.


The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors, Alexandr Rafailov, MD, and Mark A Silverberg, MD, to the development and writing of this article.

  1. White J. CSL Antivenom Handbook. 2nd ed. 2001. Available at

  2. Nimorakiotakis B, Winkel KD. Spider bite--the redback spider and its relatives. Aust Fam Physician. 2004 Mar. 33(3):153-7. [Medline]. [Full Text].

  3. Graudins A. Widow spider envenomation: Lactrodectism. Dart RC, ed. Medical Toxicology. 3rd ed. Lippincott Williams & Wilkins; 2003. 1592-1595/248. [Full Text].

  4. Nicholson GM, Graudins A. Spiders of medical importance in the Asia-Pacific: atracotoxin, latrotoxin and related spider neurotoxins. Clin Exp Pharmacol Physiol. 2002 Sep. 29(9):785-94. [Medline].

  5. Ushkaryov YA, Volynski KE, Ashton AC. The multiple actions of black widow spider toxins and their selective use in neurosecretion studies. Toxicon. 2004 Apr. 43(5):527-42. [Medline].

  6. Mollison L, Liew D, McDermott R, Hatch F. Red-back spider envenomation in the red centre of Australia. Med J Aust. 1994 Dec 5-19. 161(11-12):701, 704-5. [Medline].

  7. Isbister GK, Gray MR. Latrodectism: a prospective cohort study of bites by formally identified redback spiders. Med J Aust. 2003 Oct 20. 179(8):455; author 455-6. [Medline].

  8. Sutherland SK, Trinca JC. Survey of 2144 cases of red-back spider bites: Australia and New Zealand, 1963--1976. Med J Aust. 1978 Dec 30. 2(14):620-3. [Medline].

  9. Bush SP. Black widow spider envenomation mimicking cholecystitis. Am J Emerg Med. 1999 May. 17(3):315. [Medline].

  10. Ward TR, Falconer JA, Craven JA. An irritable infant and the runaway redback: an instructive case. Case Rep Emerg Med. 2011. 2011:125740. [Medline]. [Full Text].

  11. Dzelalija B, Medic A. Latrodectus bites in northern Dalmatia, Croatia: clinical, laboratory, epidemiological, and therapeutical aspects. Croat Med J. 2003 Apr. 44(2):135-8. [Medline].

  12. White J. Envenoming and antivenom use in Australia. Toxicon. 1998 Nov. 36(11):1483-92. [Medline].

  13. Dart RC, Bogdan G, Heard K, et al. A randomized, double-blind, placebo-controlled trial of a highly purified equine F(ab)2 antibody black widow spider antivenom. Ann Emerg Med. 2013 Apr. 61(4):458-67. [Medline].

  14. Isbister GK, Page CB, Buckley NA, et al. Randomized Controlled Trial of Intravenous Antivenom Versus Placebo for Latrodectism: The Second Redback Antivenom Evaluation (RAVE-II) Study. Ann Emerg Med. 2014 Jul 3. [Medline].

  15. Edmonds M. Redback Antivenom… what is everyone RAVEing on about?. Adelaide Emergency Physicians EDucation Resources. Available at Accessed: August 18, 2014.

  16. Clark RF, Wethern-Kestner S, Vance MV, Gerkin R. Clinical presentation and treatment of black widow spider envenomation: a review of 163 cases. Ann Emerg Med. 1992 Jul. 21(7):782-7. [Medline].

  17. Cohen J, Bush S. Case report: compartment syndrome after a suspected black widow spider bite. Ann Emerg Med. 2005 Apr. 45 (4):414-6. [Medline]. [Full Text].

  18. Isbister GK. Failure of intramuscular antivenom in Red-back spider envenoming. Emerg Med (Fremantle). 2002 Dec. 14(4):436-9. [Medline].

  19. Isbister GK, Brown SG, Miller M, Tankel A, Macdonald E, Stokes B, et al. A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism--the RAVE study. QJM. 2008 Jul. 101(7):557-65. [Medline].

  20. Australian Museum. Available at

  21. Hahn IH. Chapter 119: Arthropods. Flomenbaum NE, Goldfrank LR, Hoffman RS, Howland MA, Lewin NA, Nelson LS, eds. Goldfrank's Toxicologic Emergencies. 9th ed. New York, NY: McGraw-Hill; 2010. 1561-1581.

Female redback spider showing a distinctive red stripe over the abdomen. Image courtesy of John Paterson.
Female redback spider with egg sacs. Image courtesy of John Paterson.
Female redback spider. Image courtesy of John Paterson.
Female redback spider. Image courtesy of John Paterson.
All material on this website is protected by copyright, Copyright © 1994-2016 by WebMD LLC. This website also contains material copyrighted by 3rd parties.