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Fire Ant, Brown Recluse Spider, Black Widow Spider and Scorpion Envenomations

Continuing Medical Education

This CME article will review the diagnosis and treatment of envenomations of four venomous creatures; fire ants, brown recluse spiders, black widow spiders and scorpions.

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By Stuart M. Caplen, MD

Fire Ants

Fire ants floating in flood water

Fire ants first were found in the United States in the 1930s. Now there are five times more fire ants per acre in the U.S. than in South America, as they escaped their natural enemies and thrived in the southern U.S.[1] There are two types of fire ants; the red fire ant named Solenopsis invicta and the black named Solenopsis richteri.[2] Red fire ants are typically found in the southeast from Texas to North Carolina. There are areas of New Mexico, Arizona and California that are also infested.[1] The black fire ant is found in northern Alabama, northern Mississippi, and southern Tennessee.[2] Fire ants are remarkably hardy and can even form floating life rafts made of thousands of ants in times of flooding.[3]...

The CME and CONCLUSION includes more information about fire ant venom, fire ant envenomation, and treatment.

Brown recluse spider with violin marking on dorsum

Brown Recluse Spiders

The brown recluse spider or Loxosceles reclusa, is found mainly in the Midwest and Southcentral regions of the U.S.[5] It is also called the violin or fiddleback spider because of a violin-shaped marking on its back. An adult brown recluse spider with its legs extended is about 1 to 1.5 inches long.[6] They prefer dark areas such as under tree bark and rocks. Indoors they may be found in attics, closets, drawers or under bed sheets. These spiders generally only bite as a defense mechanism when they are crushed or pressed on.[5]...

The CME and CONCLUSION includes more information about brown recluse venom, envenomation, how to diagnosis a brown recluse spider bite, and treatment.

Black Widow Spiders

Black widow spider with typical hourglass marking

In North America the Latrodectus species or black widow spider is a cause of significant envenomation. The spider can be identified by its black body and red hourglass-shaped marking on the abdomen. The black widow moniker results from observation of the female frequently devouring the male after a mating session. Black widow spiders typically range from 0.5 to 1.5 inches in length[20] and have fangs and venom. The female has larger venom glands, longer fangs, and can be many times larger in size than the male and as such is more of a threat to humans. Males may have red or yellow spots or bands on the back rather than an hourglass-shaped marking.[20]...

The CME and CONCLUSION includes information about black widow spider venom, envenomation, and treatment.


Poison control centers in the United States receive close to 17,000 reports of scorpion envenomations per year.[28] There are over 1,700 scorpion species around the world but only 25 are lethal to humans. In the United States there are a number of different species but there are two that cause most significant envenomations. The most common is Centruroides sculpturatus, followed by Centruroides vittatus.[29] There has been some taxonomic confusion in the past with Centruroides sculpturatus and Centruroides exilicauda being considered the same species and the names used interchangeably in the literature. However, research has concluded they are two separate species.[30] The Centruroides sculpturatus is also known as a bark scorpion for its ability to climb and can be found in trees, rock walls or house walls as well as under rocks or in crevices. The Centruroides vittatus is also known as the striped bark scorpion due to the marking on its back. Both species are found in Arizona, New Mexico, Texas, California, Utah, Nevada, and in adjacent areas of Mexico.[31.32] The Centruroides exilicauda is found in ...

The CME and CONCLUSION has more information about scorpion venom, envenomation, and treatment.


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Stuart M. Caplen, MD, FACEP, MSM

Dr. Caplen is a retired emergency medicine physician and former emergency department medical director, who also has a Master of Science in Management degree, and green belt certification in Lean/Six Sigma.


[1]Fire Ants. CDC. Last reviewed: May 31, 2018. Retrieved from:

[2]Kruse B, Anderson J, Simon LV. Fire Ant Bites. [Updated 2020 Aug 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan. Retrieved from:

[3]Zhang S. Yes, That's a Huge Floating Mass of Live Fire Ants in Texas. The Atlantic. August 29, 2017. Retrieved from:

[4]Insect Sting Allergy. American College of Allergy, Asthma, and Immunology. Last updated 2/5/2018. Retrieved from:

[5] Anoka IA, Robb EL, Baker MB. Brown Recluse Spider Toxicity. [Updated 2020 Aug 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; Last Update: August 10, 2020. Retrieved from:

[6]Potter MF. Brown Recluse Spider. University of Kentucky College of Agriculture, Food and Environment. Last revised 7/12/18. Retrieved from:

[7]Stoecker WV, Vetter RS, Dyer JA. NOT RECLUSE—A Mnemonic Device to Avoid False Diagnoses of Brown Recluse Spider Bites. JAMA Dermatol. 2017;153(5):377–378. Retrieved from:

[8] Merchant ML, Hinton JF, Geren CR. Sphingomyelinase D activity of brown recluse spider (Loxosceles reclusa) venom as studied by 31P-NMR: effects on the time-course of sphingomyelin hydrolysis. Toxicon. 1998 Mar;36(3):537-45. Retrieved from:

[9] Wilson JR et al. Brown Recluse Spider Bites: A Complex Problem Wound. A Brief Review and Case Study. Wound Care Learning Network. March 2005. Retrieved from:

[10] Carlton Jr. PK. Brown recluse spider bite? Consider this uniquely conservative treatment -An antihistamine and observation work as well—and often better—than more intensive therapies. The Journal of Family Practice. Vol 58, No. 2. February 2009. Retrieved from:

[11]Tavener B. Biting back: Taking the sting out of spider venom. BBCNews. 3 August 2013. Retrieved from:

[12]Ree R et al. Annals of emergency Medicine. The Diagnosis and Treatment of Brown Recluse Spider Bites. 16:9 September 1987. Retrieved from:

[13]Rees, R S et al. “Brown recluse spider bites. A comparison of early surgical excision versus dapsone and delayed surgical excision.” Annals of surgery vol. 202,5 (1985): 659-63. Retrieved from:

[14] King LE, Rees RS. Dapsone Treatment of a Brown Recluse Bite. JAMA. 1983;250(5):648. Retrieved from:

[15]Forks TP. Brown Recluse Spider Bites. J Am Board Fam Pract 2000;13:415-23. Retrieved from:

[16]Maynor ML, Moon RE, Klitzman B, Fracica PJ, Canada A. Brown recluse spider envenomation: a prospective trial of hyperbaric oxygen therapy. Acad Emerg Med. 1997 Mar;4(3):184-92. Retrieved from:

[17]Phillips S, Kohn M, Baker D, et al. Therapy of brown spider envenomation: a controlled trial of hyperbaric oxygen, dapsone, and cyproheptadine. Ann Emerg Med 1995;25:363-8. Retrieved from:

[18]Strain GM, Snider TG, Tedford BL, Cohn GH. Hyperbaric oxygen effects on brown recluse spider (Loxosceles reclusa) envenomation in rabbits. Toxicon. 1991;29(8):989-96. Retrieved from:

[19]Hadanny A, Fishlev G, Bechor Y, Meir O, Efrati S. Nonhealing Wounds Caused by Brown Spider Bites: Application of Hyperbaric Oxygen Therapy. Adv Skin Wound Care. 2016 Dec;29(12):560-566. Retrieved from:

[20]Vail KM, et al. The Black Widow Spider. Agricultural Extension Service, The University of Tennessee. 2002. Retrieved from:

[21]Williams M, Anderson J, Nappe TM. Black Widow Spider Toxicity. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from:

[22]Diaz, JH, Leblanc KM. Common Spider Bites. American Family Physician. 2007 Mar 15;75(6):869-873. Retrieved from:

[23]Monte AA, Bucher-Bartelson B, Heard KJ. A US perspective of symptomatic Latrodectus spp. envenomation and treatment: a National Poison Data System review. Ann Pharmacother. 2011 Dec;45(12):1491-8. Retrieved from:

[24]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. Retrieved from:

[25]ANTIVENIN, (LATRODECTUS MACTANS)(Black Widow Spider Antivenin). Merck and Co. 2020. Retrieved from:

[26]Dart RC et al. The Efficacy of Antivenin Latrodectus (Black Widow) Equine Immune F(ab')2 Versus Placebo in the Treatment of Latrodectism: A Randomized, Double-Blind, Placebo-Controlled, Clinical Trial. Ann Emerg Med. 2019 Sep;74(3):439-449. Retrieved from:

[27]Rare Disease Therapeutics, Inc. Retrieved from: on Sept. 14, 2021.

[28]Kang, A Min, and Daniel E Brooks. “Nationwide Scorpion Exposures Reported to US Poison Control Centers from 2005 to 2015.” Journal of medical toxicology : official journal of the American College of Medical Toxicology vol. 13,2 (2017): 158-165. Retrieved from:

[29]Shamoon Z, Peterfy RJ, Hammoud S, et al. Scorpion Toxicity. [Updated 2021 Aug 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan Retrieved from:

[30]Norma A. Valdez-Cruz NA et al. Biochemical, genetic and physiological characterization of venom components from two species of scorpions: Centruroides exilicauda Wood and Centruroides sculpturatus Ewing. Biochimie, Volume 86, Issue 6, Pages 387-396. 2004. Retrieved from:

[31]Animal Fact Sheet: Bark Scorpion Arizona-Sonora Desert Museum. 2008. Retrieved from:

[32]Huang C. Scorpion's Sting. EMResident. 8/14/2014. Retrieved from:

[33]Anascorp® Centruroides (Scorpion) Immune F(ab’)2 (Equine) Package insert. July 2011. Retrieved from:

[34]Boyer LV et al. Antivenom for Critically Ill Children with Neurotoxicity from Scorpion Stings. N Engl J Med 2009; 360:2090-2098. Retrieved from:


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