Tests and diagnosisBy Mayo Clinic staff
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 eye witness 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
- Entire body, including legs, can be more than an inch (25 mm) across
- Vetter RS, et al. Approach to the patient with a suspected spider bite: An overview. http://www.uptodate.com/home. Accessed March 12, 2013.
- Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 5th ed. Edinburgh, U.K.; New York, N.Y.: Mosby Elsevier; 2010. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-0-7234-3541-9..X0001-6--TOP&isbn=978-0-7234-3541-9&uniqId=230100505-57. Accessed March 12, 2013.
- Spider bites. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/injuries_poisoning/bites_and_stings/spider_bites.html?qt=spider bites&alt=sh. Accessed March 14, 2013.
- Kliegman RM, et al. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa.: Saunders Elsevier; 2011. http://www.mdconsult.com/das/book/body/208746819-6/0/1608/0.html. Accessed March 12, 2013.
- Venomous spiders. National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/topics/spiders. Accessed March 12, 2013.
- Vetter RS, et al. Bites of widow spiders. http://www.uptodate.com/home. Accessed March 12, 2013.
- Vetter RS, et al. Bites of recluse spiders. http://www.uptodate.com/home. Accessed March 12, 2013.
- Brown recluse spider. Occupational Safety and Health Administration. http://www.osha.gov/OshDoc/data_Hurricane_Facts/brown_recluse_spider.pdf. Accessed March 15, 2013.
- Auerbach PS, et al. Wilderness Medicine. 6th ed. Philadelphia, Pa.: Mosby Elsevier; 2012. http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4377-1678-8..00052-0&isbn=978-1-4377-1678-8&sid=1418655681&uniqId=405544036-3#4-u1.0-B978-1-4377-1678-8..00052-0. Accessed March 15, 2013.