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The southern black widow spider (Latrodectus mactans), a cause of latrodectism
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Latrodectism (/lætrəˈdɛktɪzəm/) is the illness caused by the bite of Latrodectus spiders (the black widow spider and related species). Pain, muscle rigidity, vomiting, and sweating are the symptoms of latrodectism.

There are several spider species all named black widow: southern black widow spider (L. mactans), the European black widow (L. tredecimguttatus), Western black widow spider (L. hesperus), Northern black widow spider (L. variolus). Other Latrodectus that cause latrodectism are the Australian redback spider (L. hasselti), the New Zealand katipō spider (L. katipo) and the South American Latrodectus corallinus and Latrodectus curacaviensis. Several other members of the genus Latrodectus are not commonly associated with latrodectism including the cosmopolitan brown widow (L. geometricus).

Signs and symptoms[edit]

Symptoms of a bite depend on the amount of venom injected. A bite of Latrodectus may not inject any venom (known as a dry bite) and so no illness occurs. About 75% of "wet" bites will have localized pain and nothing more.[1] If, however, there is a substantial dose, a bite can cause latrodectism. The main symptoms are generalized muscle pain, stomach cramps, nausea and vomiting.[2][3] Initially a pinprick or burning sensation can be felt when bitten by widow spiders. If there was enough venom injected, pain worsens over the next hour. The area will develop localized sweating and goosebumps. The pain may spread and become generalized.[4] The typical duration is three to six days. Rarely, some people who do not receive antivenom may have muscle weakness that lasts for weeks.[5]

Classic course[edit]

  • Intense local pain develops 5–10 minutes after the bite and is followed by sweating and piloerection (goosebumps) within an hour. Neither puncture marks nor redness are necessarily seen.
  • A few people go on to have widespread symptoms. Pain typically starts at the bite site then travels up (e.g. from foot to thigh to trunk), followed by generalized pain (in back, trunk, chest or shoulder). The venom directly affects nerves leading to the unusual feature of severe sweating, which may be regional (e.g. one leg). Changes in adrenaline can lead to mild increase in blood pressure and pulse.
  • Non-specific features of latrodectism include headache, nausea, vomiting and feeling ill and weak.
  • Symptoms may wax and wane over the next one to four days. Rarely, patients may feel unwell for up to a week. Very rarely, untreated patients report ongoing bite site pain that last weeks or months.[6]

Special circumstances[edit]

  • During pregnancy the pain and abdominal cramps may be confused with other conditions.[7][8] A case of preterm labor initiated by a redback spider was relieved by antivenom.[9]
  • Early medical reports of latrodectism were described in men using outhouses. The genitals were often the site of the bite. No direct injury to site is reported.[10]
  • Myocarditis (inflammation of the heart muscle) has been associated with one medically reported death in the last 50 years.[11]
  • Rhabdomyolysis (rapid skeletal muscle tissue breakdown) is an uncommon complication.[12]


Spider venoms are a complex collection of toxic agents. Unique to the widows is latrotoxin. The venom acts on nerves causing the massive release of the neurotransmitters acetylcholine, norepinephrine, and GABA. The release of these neurotransmitters leads to pain, cramps, sweating and fast pulse.[13] Latrotoxin acts on presynaptic nerve membranes (See Chemical synapse) and through the cell's signalling protein (calcium-independent receptor of alpha-latrotoxin CIRL).[14] Thus initial pain is often followed by severe muscle cramps. Contraction of musculature may extend throughout the body, though cramping in the abdomen is frequently the most severe. Latrotoxin may act on muscles directly preventing relaxation, promoting tetany—constant, strong, and painful muscle contractions.[citation needed]


There are no tests required to diagnose widow spider bites, or latrodectism symptoms.[4][5] The diagnosis is clinical and based on historic evidence of widow spider bites. Pathognomonic symptoms such as localized sweating and piloerection provide evidence of envenomation. Diagnosis in most people includes reporting contact with a Latrodectus spider. Overdiagnosis is a risk, without a spider to identify. However, without a history of contact, the diagnosis may be missed as symptoms overlap with a variety of other serious clinical syndromes such as tetanus or acute abdomen. Blood values are typically unimportant but may be needed to show myocarditis or dehydration from vomiting.[4][5]


People who have been bitten by a black widow spider are recommended to seek professional medical assistance for symptoms.[15] Symptoms self-resolve in hours to days in a majority of bites without medical intervention.

Medical treatments have varied over the years. Some treatments (e.g. calcium gluconate) have been discovered to be useless.[16] Currently, treatment usually involves symptomatic therapy with pain medication, muscle relaxants, and antivenom. When the pain becomes unbearable, antivenom is administered. Antivenom historically completely resolves pain in a short time.[4][17] Antivenom is made by injecting horses with latrodectus venom over a period of time. The horse develops antibodies against the venom. The horse is bled and the antibodies purified for later use. Doctors recommend the use of anti-inflammatory medications before antivenom administration, because antivenom can induce allergic reactions to the horse proteins.[4] The efficacy of antivenom has come under scrutiny as patients receiving placebo have also recovered quickly.[18][19] Antivenom is used widely in Australia for redback bites; however, in the United States, it is less commonly used. Antivenom made from spider bite survivors has been used since the 1920s.[10] Opioids such as morphine relieve pain and benzodiazepines ease muscle spasm in most patients.[16]


The vast majority of victims fully recover without significant lasting problems. Death from latrodectism is rare and primarily occurs in adults with cardiovascuar disease or children.[2][20] In the United States, where antivenom is rarely used, there have been no deaths reported for decades.[21]

Despite a frequent reference to youth and old age being predisposing factors, it has been demonstrated that young children appear to be at the lowest risk for a serious bite, perhaps owing to the rapid use of antivenom.[22] Bite victims who are very young, old, hypotensive, pregnant, or who have existing heart problems are reported to be the most likely to develop complications.[citation needed]


Bites from Latrodectus occur usually because of accidental contact with the spiders. The species are not aggressive to humans naturally, but may bite when trapped. As such, bite incidents may be described as accidents. Reports of epidemics[23] were associated with agricultural areas in Europe in the last two centuries. However the European spider is associated with fields and humans come in contact only during harvest. For example, in the 1950s researchers believed that three bites happened each year and with an epidemic up to 180 each year.[24]

Conversely, redback and North American black widows live in proximity with people and several hundred black widow bites are reported to Poison Control in the United States each year. Of the bites reported in the United States from 2001 to 2005, approximately 31% were treated in a health care facility, 0.5% had major complications, and none were fatal.[25]

In Perth, Australia, for example there were 156 bites in children from redback spiders over 20 years. Twice as many boys were bitten as girls, mostly toddlers. A third of the children developed latrodectism and there were no deaths.[26]

See also[edit]


  1. ^ Vetter Richard S., Isbister Geoffrey K. (2008). "Medical aspects of spider bites". Annual Review of Entomology. 53: 409–429. doi:10.1146/annurev.ento.53.103106.093503. PMID 17877450.
  2. ^ a b Timms, P. K.; Gibbons, R. B. (March 1986). "Latrodectism—effects of the black widow spider bite". Western Journal of Medicine. 144 (3): 315–317. PMC 1306604. PMID 3962294.
  3. ^ Ushkaryov, YA; Rohou, A; Sugita, S (2008). "α-Latrotoxin and iItsReceptors". Pharmacology of Neurotransmitter Release. Handbook of Experimental Pharmacology. Vol. 184. pp. 171–206. doi:10.1007/978-3-540-74805-2_7. ISBN 978-3-540-74804-5. PMC 2519134. PMID 18064415.
  4. ^ a b c d e Jelinek, GA (November 1997). "Widow spider envenomation (latrodectism): a worldwide problem". Wilderness & Environmental Medicine. 8 (4): 226–31. doi:10.1580/1080-6032(1997)008[0226:WSELAW]2.3.CO;2. PMID 11990169.
  5. ^ a b c Peterson, ME (November 2006). "Black widow spider envenomation". Clinical Techniques in Small Animal Practice. 21 (4): 187–90. doi:10.1053/j.ctsap.2006.10.003. PMID 17265903.
  6. ^ "Unsupported Browser".
  7. ^ Sherman Roger P.; et al. (2000). "Black widow spider (Latrodectus mactans) envenomation in a term pregnancy". Current Surgery. 57 (4): 346–348. doi:10.1016/s0149-7944(00)00276-2. PMID 11024247.
  8. ^ Langley Ricky Lee (2004). "A review of venomous animal bites and stings in pregnant patients". Wilderness & Environmental Medicine. 15 (3): 207–215. doi:10.1580/1080-6032(2004)15[207:arovab];2. PMID 15473462.
  9. ^ KNOX, IAN, and DON CAVE. "Premature labor precipitated by red‐back spider envenomation." Emergency Medicine 5.1 (1993): 3–5.
  10. ^ a b Bogen Emil (1926). "Arachnidism: spider poisoning". Archives of Internal Medicine. 38 (5): 623–632. doi:10.1001/archinte.1926.00120290072008.
  11. ^ González Valverde FM; et al. (2001). "Fatal latrodectism in an elderly man". Medicina Clinica. 117 (8): 319. doi:10.1016/s0025-7753(01)72100-8. PMID 11571130.
  12. ^ Vetter, Richard S., et al. "Bites of widow spiders". (2013).
  13. ^ Meier J, White J, eds. (1995). Handbook of clinical toxicology of animal venoms and poisons. CRC Press. ISBN 978-0-8493-4489-3.
  14. ^ Krasnoperov, V. G.; Bittner, M. A.; Beavis, R; Kuang, Y; Salnikow, K. V.; Chepurny, O. G.; Little, A. R.; Plotnikov, A. N.; Wu, D; Holz, R. W.; Petrenko, A. G. (1997). "Alpha-Latrotoxin stimulates exocytosis by the interaction with a neuronal G-protein-coupled receptor". Neuron. 18 (6): 925–37. doi:10.1016/s0896-6273(00)80332-3. PMID 9208860.
  15. ^ "Spider bites - Diagnosis and treatment - Mayo Clinic". Mayo Clinic.
  16. ^ a b Prongay, R; Kelsberg, G; Safranek, S (November 2012). "Clinical inquiry: which treatments relieve painful muscle spasms from a black widow spider bite?". The Journal of Family Practice. 61 (11): 694–5. PMID 23256102.
  17. ^ Rohou, A; Nield, J; Ushkaryov, YA (2007-03-15). "Insecticidal toxins from black widow spider venom". Toxicon. 49 (4): 531–49. doi:10.1016/j.toxicon.2006.11.021. PMC 2517654. PMID 17210168.
  18. ^ Isbister, Geoffrey K.; Page, Colin B.; Buckley, Nicholas A.; Fatovich, Daniel M.; Pascu, Ovidiu; MacDonald, Stephen P.J.; Calver, Leonie A.; Brown, Simon G.A. (December 2014). "Randomized Controlled Trial of Intravenous Antivenom Versus Placebo for Latrodectism: The Second Redback Antivenom Evaluation (RAVE-II) Study". Annals of Emergency Medicine. 64 (6): 620–628.e2. doi:10.1016/j.annemergmed.2014.06.006. hdl:2123/14928. PMID 24999282.
  19. ^ Isbister, G.K.; Brown, S.G.A.; Miller, M.; Tankel, A.; Macdonald, E.; Stokes, B.; Ellis, R.; Nagree, Y.; Wilkes, G.J.; James, R.; Short, A.; Holdgate, A. (4 March 2008). "A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism--the RAVE study". QJM. 101 (7): 557–565. doi:10.1093/qjmed/hcn048. PMID 18400776.
  20. ^ Dart, Richard C.; Bush, Sean P.; Heard, Kennon; et al. (September 2019). "The Efficacy of Antivenin Latrodectus (Black Widow) Equine Immune F(abʹ)2 Versus Placebo in the Treatment of Latrodectism: A Randomized, Double-Blind, Placebo-Controlled, Clinical Trial". Annals of Emergency Medicine. 74 (3): 439–449. doi:10.1016/j.annemergmed.2019.02.007.
  21. ^ Shackleford, Rodney; Veillon, Diana; Maxwell, Nicole; LaChance, Lisa; Jusino, Tamara; Cotelingam, James; Carrington, Patrick (March 2015). "The black widow spider bite: differential diagnosis, clinical manifestations, and treatment options". The Journal of the Louisiana State Medical Society. 167 (2): 74–78. ISSN 0024-6921. PMID 25978056.
  22. ^ Mead H. J., Jelinek G. A. (1993). "Red‐back spider bites to Perth children, 1979‐1988". Journal of Paediatrics and Child Health. 29 (4): 305–308. doi:10.1111/j.1440-1754.1993.tb00518.x. PMID 8373679. S2CID 25640556.
  23. ^ Bettini Sergio (1964). "Epidemiology of latrodectism". Toxicon. 2 (2): 93–102. doi:10.1016/0041-0101(64)90009-1. PMID 14301291.
  24. ^ Bettini, Sergio (1 October 1964). "Epidemiology of latrodectism". Toxicon. 2 (2): 93–102. doi:10.1016/0041-0101(64)90009-1. PMID 14301291.
  25. ^ Langley Ricky L (2008). "Animal bites and stings reported by United States poison control centers, 2001–2005". Wilderness & Environmental Medicine. 19 (1): 7–14. doi:10.1580/07-weme-or-111.1. PMID 18333665.
  26. ^ MEAD, H. J.; JELINEK, G. A. (August 1993). "Red-back spider bites to Perth children, 1979–1988". Journal of Paediatrics and Child Health. 29 (4): 305–308. doi:10.1111/j.1440-1754.1993.tb00518.x. PMID 8373679. S2CID 25640556.

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