Diagnosis

Your doctor may suspect a spider bite based on your history and your signs and symptoms, but a specific diagnosis is difficult to confirm. Confirmation requires:

  • An eyewitness to the bite
  • Identification of the spider by an expert
  • Exclusion of other possible causes

Black widow identification

Some clues for identifying black widow spiders include:

  • Shiny black body
  • Large round abdomen
  • Red hourglass on underside of abdominal area
  • Central body about a half-inch (12 to 13 millimeters) long
  • Entire body, including legs, can be more than an inch (2.5 centimeters) across

Brown recluse identification

Some clues for identifying brown recluse spiders include:

  • Color ranges from yellowish tan to dark brown
  • Dark violin shape on top of the leg attachment segment
  • Six eyes — a pair in front and a pair on both sides — rather than the usual spider pattern of eight eyes in two rows of four
  • Central body is a quarter-inch to three-quarters of an inch (6 to 19 mm) long
May 14, 2016
References
  1. Vetter RS, et al. Approach to the patient with a suspected spider bite: An overview. http://www.uptodate.com/home. Accessed March 8, 2016.
  2. Habif TP. Infestations and bites. In: Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 6th ed. Edinburgh, U.K.; New York, N.Y.: Mosby Elsevier; 2016. https://www.clinicalkey.com. Accessed March 8, 2016.
  3. Spider bites. Merck Manual Professional Version. http://www.merckmanuals.com/professional/SearchResults?query=spider+bites. Accessed March 8, 2016.
  4. Venomous spiders. National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/topics/spiders. Accessed March 8, 2016.
  5. Vetter RS, et al. Management of widow spider bites. http://www.uptodate.com/home. Accessed March 8, 2016.
  6. Vetter RS, et al. Bites of recluse spiders. http://www.uptodate.com/home. Accessed March 8, 2016.
  7. Brown recluse spider. Occupational Safety and Health Administration. http://www.osha.gov/OshDoc/data_Hurricane_Facts/brown_recluse_spider.pdf. Accessed March 8, 2016.
  8. Diaz JH, et al. Common spider bites. American Family Physician. 2007;75:869.
  9. Claypool DW (expert opinion). Mayo Clinic, Rochester, Minn. Nov. 24, 2014.
  10. Juckett G. Arthropod bites. American Family Physician. 2013;88:841.
  11. Black widow spider. Occupational Safety and Health Administration. http:www.osha.gov/OshDoc/data_Hurricane_Facts/black_widow_spider.pdf. Accessed March 23, 2016.