Spider Bite  
Back to Index

Does this describe your symptoms?

Click image for
more info
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┬áthe skin instead became infected with a bacteria called Staphylococcus aureus (MRSA).

Black Widow Spider Bite

  • Description: A shiny, jet-black spider with long legs (total size 1 inch). A red (or orange) hourglass-shaped marking may be on its under-side (not present in all Lactrodectus species).
  • Habitat: Found throughout North America, except Alaska and the far North.
  • Symptoms - Bite Wound: The black widow spider produces one of nature's most potent neurotoxic venoms. The bite causes immediate moderate to severe pain; there is usually minimal to no local reaction.
  • Symptoms - Systemic: Severe muscle cramps are present by 1 to 6 hours, and last 24 to 48 hours. Other possible symptoms include abdominal pain, vomiting, restlessness, hypertension, and weakness.
  • Treatment - Local Wound Care: Wash bite with soap and water. Apply an ice pack.
  • Treatment - Medications: Tetanus prophylaxis should be provided. Parenteral analgesics may be needed for pain and benzodiazepines for muscle spasms. There is a Lactrodectus antivenin that is indicated for severe symptoms, seizures, or uncontrolled hypertension.
  • Expected Course: All symptoms usually resolve over 2-3 days. Death may occur rarely; a bite is more serious in a small child; multiple spider bites are also more serious.
  • Special Note: Many bite wounds are "dry bites" (no venom injected into skin) because the fangs are small.

Brown Recluse Spider Bite

  • Also known as the "violin" or "fiddleback" spider.
  • Description: A brown spider with long legs (total size 1/2 inch). dark violin-shaped marking on top of its head (not present in all Loxosceles species).
  • Habitat: Found in the southern, southwestern and midwestern United States.
  • Symptoms - Bite Wound: The spider produces a venom which causes cell destruction and blood cell breakdown. The bite is initially painless or minimally painful. Local pain and blister formation develops in 4 to 8 hours. The center becomes bluish and depressed (crater-like) over 2 to 3 days. A deep necrotic ulcer may develop.
  • Symptoms - Systemic: Systemic symptoms include fever, vomiting, and myalgias (but no life-threatening symptoms).
  • Treatment - Local Wound Care: Cleansing of wound with soap and water, cold pack.
  • Treatment - Medications: Tetanus prophylaxis should be provided.
  • Expected Course: Most necrotic ulcers heal over one to eight weeks. Permanent scarring occurs in 10-15 percent. Skin damage sometimes requires skin grafting.


  • Habitat: Tarantulas are found in the southern United States (e.g., Desert Southwest).
  • Symptoms - Bite Wound: Mild stinging with minimal local inflammation. No skin necrosis occurs.
  • Symptoms - Eye: Some genera of tarantula have "urticating" hairs that can come off. Like a little piece of fiberglass, they can penetrate human skin and cause itching and redness. If they lodge in the cornea they can cause foreign body keratoconjunctivitis or ophthalmia nodosa.
  • Symptoms - Systemic: None.
  • Treatment - Local Wound Care: Cleansing of bite wound with soap and water, cold pack, oral analgesics. Obtaining a tetanus booster is appropriate if it has been longer than 10 years.
  • Treatment - Eye Irritation: Individuals with eye irritation or redness after handling a tarantula should be referred to an ophthalmologist for a slit lamp examination of the eye,
  • Expected Course: Bite wounds heal completely. Eye problems generally resolve under the close follow-up care of an ophthalmologist.

Minor (Non-Dangerous) Spider Bites

  • More than 50 spiders in the U.S. and Canada have venom and can cause minor, localized, non-serious reactions. Many single, unseen and unexplained painful bites that occur during the night can be due to spiders.
  • Symptoms - Bite Wound: The bites are painful and mildly swollen for 1 or 2 days (much like a bee sting).
  • Symptoms - Systemic: None.
  • Treatment - Local Wound Care: Cleansing of bite wound with soap and water, cold pack, oral analgesics. Obtaining a tetanus booster is appropriate if it has been longer than 10 years.
  • Expected Course: Bite wounds heal completely.

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 (or brown widow) spider bite
  • Abdominal pain, chest tightness or other muscle cramps
  • Vomiting
  • Urine is brown, black or red in color
  • Severe bite pain and not improved after 2 hours of pain medicine
  • Redness, red streak, or very tender area (to touch), and you also have a fever
Call Your Doctor Within 24 Hours (between 9 am and 4 pm) If
  • You think you need to be seen
  • Red or very tender (to touch) area, and started over 24 hours after the bite
  • Red or very tender (to touch) area, getting larger over 48 hours after the bite
  • Diabetic and spider bite of foot
  • Bite starts to look bad (e.g., blister, purplish skin, ulcer)
  • Eye irritation after handling or touching a tarantula
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

Non-Serious Spider Bite
  1. Cleansing: Wash the bite thoroughly with soap and water.
  2. Pain Medicines:
    • For pain relief, take acetaminophen, ibuprofen, or naproxen.
    Acetaminophen (e.g., Tylenol):
    • Take 650 mg by mouth every 4-6 hours. Each Regular Strength Tylenol pill has 325 mg of acetaminophen.
    • Another choice is to take 1,000 mg every 8 hours. Each Extra Strength Tylenol pill has 500 mg of acetaminophen.
    • The most you should take each day is 3,000 mg.
    Ibuprofen (e.g., Motrin, Advil):
    • Take 400 mg by mouth every 6 hours.
    • Another choice is to take 600 mg by mouth every 8 hours.
    • Use the lowest amount that makes your pain feel better.
    Naproxen (e.g., Aleve):
    • Take 250-500 mg by mouth every 12 hours.
    • Use the lowest amount that makes your pain feel better.
    Extra Notes:
    • Acetaminophen is thought to be safer than ibuprofen or naproxen in people over 65 years old. Acetaminophen is in many OTC and prescription medicines. It might be in more than one medicine that you are taking. You need to be careful and not take an overdose. An acetaminophen overdose can hurt the liver.
    • Caution: Do not take acetaminophen if you have liver disease.
    • Caution: Do not take ibuprofen or naproxen if you have stomach problems, kidney disease, are pregnant, or have been told by your doctor to avoid this type of medicine. Do not take ibuprofen or naproxen for more than 7 days without consulting your doctor.
    • Before taking any medicine, read all the instructions on the package
  3. Expected Course: Some swelling and pain for 1 to 2 days. It shouldn't be any worse than a bee sting.
  4. 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
Preventing Spider Bites
  1. Prevention - Outdoors:
    • Be especially careful around wood piles and when clearing brush.
    • Wear long pants with the pants tucked into your socks.
    • Wear long-sleeved shirts and use gloves.
    • DEET is a very effective insect repellent. It also repels spiders.
  2. Prevention - Indoors:
    • Remove spider webs.
    • Make certain that doorways and windows are effectively sealed and insulated.
  3. Using DEET-Containing Insect Repellents When Outdoors:
    • DEET is a very effective insect repellent. It also repels spiders.
    • Higher concentrations of DEET do work better - but there appears to be no benefit in using DEET concentrations above 50%. For children and adolescents, the American Academy of Pediatrics recommends a maximum concentration of 30%. Health Canada recommends using a concentration of 5-30% for adults.
    • Apply to exposed areas of skin. Do not apply to eyes, mouth or irritated areas of skin. Do not apply to skin that is covered by clothing.
    • Remember to wash it off with soap and water when you return indoors.
    • DEET can damage clothing made of synthetic fibers, plastics (e.g., eye glasses), and leather.
    • Breastfeeding women may use DEET. No problems have been reported. (CDC 2003)

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: 11/18/2011

Last Revised: 11/19/2011

Content Set: Adult HouseCalls Symptom Checker

Copyright 2000-2012. Self Care Decisions LLC; LMS, Inc.