When Should I Be Concerned About a Spider Bite?

Reviewed on 10/12/2021

Spider bites from two types of spiders, black widow spiders and brown recluse spiders, can be dangerous. Seek medical attention for a spider bite if there is a worsening local reaction for more than 24 hours, redness spreading away from the bite, drainage from the bite, increased pain, numbness/tingling, a halo or bull's eye discoloration around the bite, or an allergic reaction (rare).
Spider bites from two types of spiders, black widow spiders and brown recluse spiders, can be dangerous. Seek medical attention for a spider bite if there is a worsening local reaction for more than 24 hours, redness spreading away from the bite, drainage from the bite, increased pain, numbness/tingling, a halo or bull's eye discoloration around the bite, or an allergic reaction (rare).

Most of the time, spider bites are harmless and do not require any medical treatment. If spiders do bite, which is not common, most spiders are too small to break human skin with their fangs, or their venom is too weak to be toxic to humans.

Spider bites also rarely transmit infectious diseases and the risk of bacterial infection from a spider bite is very low.

There are some cases in which you should be concerned about a spider bite. Bites from larger spiders can be painful, but the big concern is certain spider’s venom, which can be toxic. 

What types of spiders are dangerous?

The two types of spiders that are cause for concern in the United States are the black widow spider and the brown recluse spider. Both of these types of spiders are usually timid and not aggressive, but may bite if their web or nesting place is disturbed, or if they feel threatened, especially after laying eggs. 

  • Black widow spiders 
    • Found throughout the U.S.
    • Are black or brown color with a leg span of about one to two inches and a red hourglass marking on the abdomen (usually the female, which is more dangerous)
    • Black widow spider toxin causes nerve cell dysfunction and muscle cell twitching
    • Black widow bites are less common than brown recluse bites, but more severe, however, no deaths due to black widow spiders have been reported to the American Association of Poison Control Centers since 1983
  • Brown recluse spiders 
    • Found primarily in the south central U.S. 
    • Are tan to dark brown color with a leg span of approximately 1 inch and many have a violin-shaped marking on the chest
    • Human contact with these spiders is usually accidental
    • Bites occur more often than black widow spider bites

Seek medical attention for a spider bite if there is: 

  • A local reaction that continues to worsen for more than 24 hours
  • Redness spreading away from the bite
  • Drainage from the bite
  • Increased pain
  • Numbness/tingling
  • Discoloration around the bite that looks like a halo or bull's-eye
  • An allergic reaction (rare)

What Do Spider Bites Look Like?

Common general symptoms of spider bites include: 

  • Pain
    • Usually less severe than a bee sting
    • If the bite is from a non-venomous spider, the pain lasts for 5 minutes to an hour
    • Pain from a venomous spider bite can last longer than 24 hours
  • Redness
  • Swelling
  • Itching 
  • Rash

Symptoms of black widow spider bites include: 

Symptoms of brown recluse bites include: 

  • Tenderness 
  • Stinging
  • Intense pain
  • Redness
  • Black coloration of the wound after a few days
  • Local swelling
  • Itching
  • Blisters that slough off to leave a deep ulcer which can cause tissue death (necrosis) in the area of the bite

Symptoms of an allergic reaction

  • Fever
  • Chills
  • Rash
  • Nausea
  • Vomiting
  • Kidney failure
  • Blood clotting problems 
  • Difficulty breathing
  • Death 

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What Is the Treatment for Spider Bites?

If you have been bitten by a spider, try to bring the spider with you to the doctor for identification. Treatment may depend on the type of spider. 

Treatment for non-venomous spider bites includes: 

  • Clean the spider bite with soap and water
  • Apply a cool compress over the spider bite 
  • Over-the-counter (OTC) pain relievers such as aspirin, ibuprofen (Advil, Motrin), or acetaminophen (Tylenol)
    • Children under 18 years of age should not be given aspirin due to the risk of a serious illness called Reye’s syndrome
  • Antihistamines to relieve symptoms 

Treatment of black widow and brown recluse spider bites depends on the severity of symptoms. 

Treatment for black widow spider bites includes: 

  • Clean the bite with soap and water
  • Apply cold packs to the area of the bites
  • Pain medication (bites are often painful)
    • Acetaminophen (Tylenol) or ibuprofen (Advil, Motrin)
    • Narcotics may be prescribed
  • Muscle relaxers for muscle spasms
  • Anti-nausea medications
  • Intravenous fluids
  • Tetanus booster if needed
  • Antibiotics, if there are signs of infection

Some black widow bites cause severe symptoms and require hospitalization. 

Treatment for brown recluse spider bites includes:

  • Clean the bite with soap and water
  • Apply cold packs to the area of the bites
  • Pain medication 
    • Over-the-counter (OTC) acetaminophen (Tylenol) or ibuprofen (Motrin, Advil)
  • Tetanus booster if needed

Antibiotics are generally not used to treat brown recluse spider bites unless infection develops. Monitor wounds closely signs of infection such as redness, swelling, pus, or dark/black skin. Death of tissue in the area of the bite (dermal necrosis) can occur due to a brown recluse spider bite which may require a consultation with a wound care specialist or surgeon.

There is an antivenom for brown recluse spider bites but it is not available in the United States.

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Reviewed on 10/12/2021
References
https://www.emedicinehealth.com/wilderness_black_widow_and_recluse_spider_bite/article_em.htm

https://www.uptodate.com/contents/management-of-widow-spider-bites?search=black%20widow%20spider%20bite%20treatment&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1

https://www.uptodate.com/contents/bites-of-recluse-spiders?search=brown%20recluse%20spider%20bite%20treatment&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H21

https://www.pestworld.org/news-hub/pest-health-hub/spider-bites/

https://www.medscape.com/answers/772196-158017/what-is-the-prevalence-of-widow-spider-envenomation