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First aid

Spider bite

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Black Widow Spider
Black Widow Spider

Brown Recluse Spider
Brown Recluse Spider

  • Bite from a spider seen on the skin
  • Onset of bite symptoms (redness, pain, swelling) and a spider is seen in close proximity

General Information

  • There are over 20,000 species of spiders in the world.
  • In the United States, there are two species that cause bites in humans of medical importance: the black widow (Lactrodectus) and the brown recluse (Loxosceles).
  • If you decide you need to see your doctor, bring the spider along in a jar for identification (brown recluse spiders are especially hard to identify).
  • Sometimes people incorrectly believe that they sustained a spider bite, when instead a minor break in the skin instead simply became infected with a bacteria called Staphylococcus aureus.

Black Widow Spider Bite

  • The black widow is shiny and black, with long legs (total width 1 inch). A red (or orange) hourglass-shaped marking may be on its underside (not present in all Lactrodectus species).
  • Black widow spiders are found throughout North America, except in Alaska and the far North.
  • Causes immediate local mild pain, swelling, and occasionally 2 fang marks. Severe muscle cramps are present by 1 to 6 hours, and last 24 to 48 hours. Rarely causes death (exception: bitten by several spiders or small child is bitten).
  • Note: many are dry bites because the fangs are small.
  • First Aid for Black Widow Spider Bites: Apply an ice cube or ice pack to the bite for 20 minutes to reduce the spread of the venom (no tourniquet).

Brown Recluse Spider Bite

  • Also known as the "violin" or "fiddleback" spider.
  • Is a brown spider with long legs (total width 1/2 inch). There is a dark violin-shaped marking on top of its head (not present in all Loxosceles species).
  • It can be found in the southern, southwestern, and midwestern United States.
  • Causes local pain and delayed blister formation in 4 to 8 hours. The center of the bite becomes bluish and depressed (crater-like) over 2 to 3 days. A deep necrotic ulcer may develop. Skin damage may require skin grafting in 10% of cases.
  • Generalized symptoms such as fever, vomiting, and muscle aches can occur (but no life-threatening symptoms).

Non-Dangerous Spider Bites

  • More than 50 spiders in the U.S. have venom and can cause local, non-serious reactions.
  • The bites are painful and mildly swollen for 1 or 2 days (much like a bee sting).
  • Most single, unexplained, tender bites that occur during the night are due to spiders.

If not, see these topics

When to Call Your Doctor

Call 911 Now (you may need an ambulance) If
  • Difficulty breathing or swallowing
  • Very weak (can't stand)
Call Your Doctor Now (night or day) If
  • You feel weak or very sick
  • Any black widow spider bite
  • Abdominal pain, chest tightness or other muscle cramps
  • Vomiting
  • Urine is brown, black or red in color
  • Bite pain is severe
  • Bite looks infected (red streaking from the bite area, yellow drainage) (Note: infection doesn't start until at least 24-48 hours after the bite. Any redness in the first 24 hours is due to venom)
Call Your Doctor Within 24 Hours (between 9 am and 4 pm) If
  • You think you need to be seen
  • Diabetic and spider bite of foot
  • Bite starts to look bad (e.g., skin damage, blister or purplish - not just swelling)
  • Bite pain persists longer than 2 days
Call Your Doctor During Weekday Office Hours If
  • You have other questions or concerns
Self Care at Home If
  • Non-serious spider bite and you don't think you need to be seen

  1. Cleansing: Wash the bite thoroughly with soap and water.
  2. Meat Tenderizer:
    • Rub the bite area with a cotton ball soaked in a meat tenderizer solution for 20 minutes (Exception: don't use near the eye). Do this just once.
    • If not available, apply an ice cube for 20 minutes.
  3. Pain Medication:
    • For pain relief, take acetaminophen or ibuprofen.
    • Acetaminophen (e.g., Tylenol): The dose is 650 mg by mouth every 4 hours or 1000 mg by mouth every 6 hours. Maximum dose per day = 4000 mg.
    • Ibuprofen (e.g., Motrin, Advil): The dose is 400 mg by mouth every 6 hours or 600 mg by mouth every 8 hours.
    • People who are over 65 Years of age: Acetaminophen is generally considered safer than ibuprofen. Acetaminophen dosing interval should be increased to every 8 hours because of reduced liver metabolism. Maximum dose per day = 3000 mg.
    • CAUTION: Do not take ibuprofen if you have stomach problems, kidney disease, are pregnant, or have been told by your doctor to avoid this type of anti-inflammatory drug. Do not take ibuprofen for more than 7 days without consulting your doctor.
    • CAUTION: Do not take acetaminophen if you have liver disease.
    • Read the package instructions thoroughly on all medications that you take.
  4. Expected Course: Some swelling and pain for 1 to 2 days. It shouldn't be any worse than a bee sting.
  5. Call Your Doctor If:
    • Severe bite pain persists longer than 2 hours after pain medicine
    • Abdominal pains or muscle spasms occur
    • Local pain lasts more than 2 days (48 hours)
    • Bite begins to look infected
    • You become worse

And remember, contact your doctor if you develop any of the "Call Your Doctor" symptoms.

Disclaimer: This information is not intended be a substitute for professional medical advice. It is provided for educational purposes only. You assume full responsibility for how you choose to use this information.

Author and Senior Reviewer: David A. Thompson, M.D.

Last Reviewed: 1/19/2009

Last Revised: 4/5/2008

Content Set: Adult HouseCalls Online

Portions Copyright 2000-2009 Self Care Decisions LLC; Copyright LMS, Inc.

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