Tests and diagnosis

By 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
May. 21, 2013

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