Back To Search Results

Black Widow Spider Toxicity

Editor: Thomas M. Nappe Updated: 8/7/2023 11:48:06 PM


The black widow spider species, also known by its biological nomenclature as the Latrodectus species is one of more than 40,000 different species of spiders. Clinically, it is one of most significant species of spiders worldwide. Within the United States, it is responsible for most of the clinically significant envenomation among all species of spiders. There are more than 30 different types of black widow spiders worldwide; however, not all species are as relevant due to their separation from human habitat.[1][2]

The genus Latrodectus derives its ubiquitous nickname “black widow” from its physical characteristics. The Black Widow, or Latrodectus mactans, is easily identified by its characteristic shiny black body and strikingly red hourglass-shaped marking on the abdomen. Interestingly, this species is well known by the phenomenon of the female spider devouring the male spider after mating, thereby making her a widow. Black widow spiders range from 5 to 15 mm (0.25 to 0.50 inch) in length. They have fangs and venomous glands sufficient to cause harm to humans. The female gender of the species is the most dangerous, compared to their male counterparts.  Females have more prominent venomous glands, longer fangs and a body size that can reach up to 20-times larger than their male counterparts.

Symptoms of envenomation range from local irritation and pain to a more systemic syndrome termed “latrodectism.” Latrodectism is characterized by variations in presentations ranging from autonomic disturbances to widespread pain and rigidity. Treatment ranges from simple analgesia to the administration of antivenom.


Register For Free And Read The Full Article
Get the answers you need instantly with the StatPearls Clinical Decision Support tool. StatPearls spent the last decade developing the largest and most updated Point-of Care resource ever developed. Earn CME/CE by searching and reading articles.
  • Dropdown arrow Search engine and full access to all medical articles
  • Dropdown arrow 10 free questions in your specialty
  • Dropdown arrow Free CME/CE Activities
  • Dropdown arrow Free daily question in your email
  • Dropdown arrow Save favorite articles to your dashboard
  • Dropdown arrow Emails offering discounts

Learn more about a Subscription to StatPearls Point-of-Care


Latrodectism is caused by the bite of a female black widow spider.[3]


Approximately 2600 Latrodectus-species exposures are reported to the National Poison Data System (NPDS) each year. Black widow spiders thrive in warmer climates, and except in Antarctica, exist on every continent. The 2 species most commonly implicated in envenomation within the United States are the Latrodectus mactans, or the southern black widow spider, and the Latrodectus hesperus, or the western black widow spider. Southern widow spiders are primarily located in the southeastern United States (including southern Ohio and Maryland). The western black widow spider is located along the western half of the United States, ranging from Canada to the north and extending southward to Mexico. Additional species in the United States include the Latrodectus variolus found in Eastern states, including New England; the Latrodectus bishopi, also found in the Southern states; and the Latrodectus geometricus, which is the brown widow found in the far Western states. The primary habitat of the black widow spider is outdoors where they are found in firewood, garages, gardening equipment, trash, outdoor equipment, outhouses, and on outdoor furniture. Exposures rise in spring months and continue to increase as the summer progresses into autumn.[4][5]


The venom of the black widow spider is a combination of biologically active proteins, peptides, and proteases. The primary toxin found in the venom of the black widow is alpha-Latrotoxin. It binds irreversibly to the protein receptors on presynaptic neurons and creates calcium ([Ca2+])-permeable channels within the lipid bilayers. This influx of [Ca2+] ions results in massive exocytosis of neurotransmitters, including acetylcholine, dopamine, norepinephrine, epinephrine, and glutamate.  It is this release of neurotransmitters which leads to the characteristic symptomatology of pain, muscle rigidity, vomiting, and sweating.[6]

History and Physical

Patients typically present within hours after the bite has occurred. Classically, the patient describes activities in which they have entered into the habitat of the black widow spider; such as hiking, camping, gardening, shopping or activities in a garage. Most often, these bites occur on the patients’ extremities and often go initially unnoticed but can also be immediately associated with pain.

Within minutes of being bitten, the area adjacent to the wound site may become painful, erythematous and edematous followed by the development of a central punctum. Fang marks may be evident. There is also a classic appearance of isolated diaphoresis within an area of central clearing. Neuromuscular symptoms, including severe muscle pain and cramping, usually occur within an hour. Increased autonomic function leading to tachycardia, tachypnea and hypertension are also associated and are often correlated with increased pain. 

Some patients may progress to latrodectism. Latrodectism refers to the systemic manifestations of a widow bite. Symptoms include diffuse muscle rigidity and cramping, tenderness and burning around the bite, truncal and abdominal tenderness, nausea, and vomiting. The diffuse pain associated with latrodectism spreads contiguously from the bite site. In other words, if the bite occurs on the ankle, the pain will progress proximally along the leg, and then to the adjacent extremity, abdomen, chest, and back. All extremities can be involved. 


The diagnosis of black widow envenomation is almost exclusively clinically established. Visualizing the bite along with its associated symptoms and obtaining a detailed history will allow accurate diagnosis. To officially confirm the diagnosis, the patient must bring in the spider after witnessing the bite. An entomologist, medical toxicologist, or another qualified specialist must then identify the spider. However, this is not necessary, and it should not be recommended to patients to capture, harm, or handle the spider. [7][8]

Historically, grading systems have been used. These grading systems can be helpful, but are not generally necessary for evaluation or treatment decisions.

In a large case series involving 23,409 exposures to black widow venom, Monte et al. found that 65% of patients presented with minor clinical effects, 33.5% moderate effects (longer duration of symptoms, treatment required) and 1.4% with major effects (life-threatening). Of the 9872 cases with at least minor effects, the most common symptoms of envenomation were dermal irritation (58.7%), erythema (28.6%), pain (17.9%), edema (13.6%) and abdominal pain (9.7%). Lab values are generally non-specific but may show an elevated white blood cell count, hematuria, and elevated liver enzymes. Other rare manifestations include rhabdomyolysis and myocarditis resulting in elevated creatine kinase and myoglobin in the blood and urine.

When chest pain is present, particularly in patients with a history of coronary artery disease, an electrocardiogram is appropriate.

Treatment / Management

The initial management for all cases of black widow envenomation includes local wound management and tetanus prophylaxis. Calcium gluconate and methocarbamol have been shown to be ineffective and are no longer recommended.

Mild envenomations which include pain at, and directly adjacent to, the wound can be further managed with oral analgesics, as needed. Management of moderate-severe envenomation, presenting as pain at the wound site with radiation and characteristic systemic symptoms, includes the use of opioids for pain management and benzodiazepines for muscle spasm control, as needed. Caution is necessary when co-administering opioids and benzodiazepines and hospital observation may be necessary. Prescribing agents from both classes at discharge is not recommended.

Black widow spider antivenom is safe and highly effective in most patients. It is effective in relieving symptoms, reducing the need for additional therapy, and decreasing admission rates. Typically, after administration and a brief period of observation, patients recover fully and can go home without complication. However, the antivenom has been associated with several severe allergic reactions that have led to precautionary assessment before antivenom administration. Most experts would recommend administration of antivenom to patients without a history of asthma or atopy, whose symptoms are not effectively treated with analgesics.[2][6]

Differential Diagnosis

The differential for black widow spider envenomation includes bites from other arthropods, as well as other causes of tachycardia, hypertension, muscle spasm, abdominal, back and chest pain. Other invertebrate envenomations or bites to consider include scorpion stings, as well as those from other spider species, namely the tarantula or brown recluse. With regard to abdominal pain, the practitioner must always consider other sources of acute abdominal pain, including but not limited to appendicitis, trauma, or other causes of acute abdominal pain. Back pain from muscle spasm or other etiology should be similarly considered. Regarding chest pain, especially as black widow bites can rarely cause troponin elevation, the practitioner must include acute coronary syndromes or myocarditis on their differential.


The prognosis for black widow bites is good. Most pain and systemic symptomatology are self-limited. Although patients may encounter long-term pain or muscle spasms after black widow bites, this phenomenon is rare. Similarly, systemic toxicity, including abdominal pain and autonomic dysfunction, is usually temporary. Recovery is usually complete within 24 to 48 hours. Finally, administration of anti-venom with a subsequent anaphylactic reaction is, as with most anaphylactic reactions, rare and usually a transient condition. Most patients can, and should, expect a full recovery after black widow envenomation.


Anaphylaxis associated with the antivenom


Consultation with a medical toxicologist is strongly encouraged.

Deterrence and Patient Education

After discharge the patient should be asked to return back to the ED if the following symptoms develop:

  • Rash
  • Joint and muscle pain
  • Hematuria
  • Enlarged nodes
  • Respiratory distress

Pearls and Other Issues

  • Latrodectus envenomations are 1 of 2 clinically relevant spider bites in North America and most cases, even when symptomatic, are self-limiting.
  • Mild symptoms of black widow envenomation include local pain and skin irritation.
  • Severe symptoms, also known as “latrodectism,” include systemic toxicity with diffuse pain, muscle spasm, and autonomic dysfunction.
  • Treatment modalities target pain (NSAIDs, opioids), muscle spasm (benzodiazepines) and systemic symptoms (supportive, anti-venom if necessary).
  • Latrodectus antivenom is a safe and highly effective treatment for most patients, provided they are properly risk-stratified. 
  • Consultation with a medical toxicologist is recommended.

Enhancing Healthcare Team Outcomes

an interprofessional approach to black widow spider envenomation 

Envenomation by a black widow spider is rare in the US and it has a varied presentation. Because of the morbidity of the bite, healthcare workers including the triage nurses must be aware of the signs and symptoms of this particular spider bite. The vast majority of patients present to the emergency department and the quicker the care provided, the better the outcome. Most patients have an eventful outcome. After discharge, the patient should be encouraged to keep pesticides in the home and/or have the home inspected for any more spiders. [9][10]


(Click Image to Enlarge)
Latrodectus spp (Colorado)
Latrodectus spp (Colorado)
Photograph by Thomas M. Nappe, DO



Al Bshabshe A, Alfaifi M, Alsayed AF. Black widow spider bites experience from tertiary care center in Saudi Arabia. Avicenna journal of medicine. 2017 Apr-Jun:7(2):51-53. doi: 10.4103/2231-0770.203606. Epub     [PubMed PMID: 28469986]


de Roodt AR, Lanari LC, Laskowicz RD, Costa de Oliveira V, Irazu LE, González A, Giambelluca L, Nicolai N, Barragán JH, Ramallo L, López RA, Lopardo J, Jensen O, Larrieu E, Calabró A, Vurcharchuc MG, Lago NR, García SI, de Titto EH, Damín CF. Toxicity of the venom of Latrodectus (Araneae: Theridiidae) spiders from different regions of Argentina and neutralization by therapeutic antivenoms. Toxicon : official journal of the International Society on Toxinology. 2017 May:130():63-72. doi: 10.1016/j.toxicon.2017.02.029. Epub 2017 Feb 27     [PubMed PMID: 28246022]


Rueda A, Realpe E, Uribe A. Toxicity evaluation and initial characterization of the venom of a Colombian Latrodectus sp. Toxicon : official journal of the International Society on Toxinology. 2017 Jan:125():53-58. doi: 10.1016/j.toxicon.2016.11.255. Epub 2016 Nov 23     [PubMed PMID: 27889602]


Goel SC, Yabrodi M, Fortenberry J. Recognition and successful treatment of priapism and suspected black widow spider bite with antivenin. Pediatric emergency care. 2014 Oct:30(10):723-4. doi: 10.1097/PEC.0000000000000235. Epub     [PubMed PMID: 25275351]

Level 3 (low-level) evidence


Madsen W, Elfar J. Spider bites. The Journal of hand surgery. 2010 Oct:35(10):1698-9. doi: 10.1016/j.jhsa.2010.07.004. Epub     [PubMed PMID: 20888508]

Level 3 (low-level) evidence


Shackleford R, Veillon D, Maxwell N, LaChance L, Jusino T, Cotelingam J, Carrington P. The black widow spider bite: differential diagnosis, clinical manifestations, and treatment options. The Journal of the Louisiana State Medical Society : official organ of the Louisiana State Medical Society. 2015 Mar-Apr:167(2):74-8     [PubMed PMID: 25978056]


Glatstein M, Carbell G, Scolnik D, Rimon A, Hoyte C. Treatment of pediatric black widow spider envenomation: A national poison center's experience. The American journal of emergency medicine. 2018 Jun:36(6):998-1002. doi: 10.1016/j.ajem.2017.11.011. Epub 2017 Nov 6     [PubMed PMID: 29133072]


Bauer J, Schaal D, Eisoldt L, Schweimer K, Schwarzinger S, Scheibel T. Acidic Residues Control the Dimerization of the N-terminal Domain of Black Widow Spiders' Major Ampullate Spidroin 1. Scientific reports. 2016 Sep 29:6():34442. doi: 10.1038/srep34442. Epub 2016 Sep 29     [PubMed PMID: 27681031]


Sotelo-Cruz N, Gómez-Rivera N. [Neurotoxic manifestations of black widow spider envenomation in paediatric patients]. Neurologia (Barcelona, Spain). 2016 May:31(4):215-22. doi: 10.1016/j.nrl.2015.05.007. Epub 2015 Aug 21     [PubMed PMID: 26304660]


Monte AA, Bucher-Bartelson B, Heard KJ. A US perspective of symptomatic Latrodectus spp. envenomation and treatment: a National Poison Data System review. The Annals of pharmacotherapy. 2011 Dec:45(12):1491-8. doi: 10.1345/aph.1Q424. Epub 2011 Nov 24     [PubMed PMID: 22116992]

Level 3 (low-level) evidence