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

Treatment

For most people with spider bites, including black widow and brown recluse spider bites, the following treatment measures are all that's required:

  • Clean the bite with mild soap and water. Apply an antibiotic ointment if you think the bite was caused by a brown recluse spider.
  • Apply a cool compress to the bite. This helps reduce pain and swelling.
  • If the bite is on an arm or leg, elevate it.
  • Take over-the-counter medications as needed. You might try a pain reliever, such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin IB, others), or an antihistamine (Benadryl, Chlor-Trimeton, others).
  • Observe the bite for signs of infection.

Your doctor may also recommend a tetanus booster shot if you haven't had one in the last five years. You may need antibiotics if the bite becomes infected.

Black widow antivenom

If a black widow bite is causing severe pain or life-threatening symptoms, your doctor may recommend an antivenom, which may be injected into a thigh muscle or given through a vein (intravenously). Antivenom can cause serious allergic reactions, so it must be used with caution.

Preparing for your appointment

If you've been bitten by a spider that you suspect is a black widow or brown recluse, call your primary care doctor or go to an urgent care center. If your doctor has online services, an option may be to email a photo of the spider to your doctor.

What you can do

To help your doctor understand your symptoms and how they might relate to a spider bite, you can:

  • Bring the spider or a photo of the spider with you
  • Write down any symptoms you're experiencing
  • Write down questions to ask your doctor

Some basic questions you might want to ask include:

  • If this is a dangerous spider bite, what's the next best step?
  • If this isn't a spider bite, what are possible causes for my symptoms or condition?
  • Do I need any tests?
  • How long will my symptoms last?
  • What is the best course of action?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

  • When did you begin experiencing symptoms?
  • What were you doing in the hours before your symptoms started?
  • Have your symptoms gotten worse?
  • Does anything relieve your symptoms or make them worse?