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Black Widow Spider Bite

Last updated March 18, 2018

Approved by: Krish Tangella MD, MBA, FCAP


The black widow spider is a medium-sized (about an inch long) venomous spider that is well-known and feared.

What are the other Names for this Condition? (Also known as/Synonyms)

  • Hourglass Spider Bite
  • Latrotoxin due to Black Widow Spider Bite
  • Neurotoxin due to Black Widow Spider Bite 

What is Black Widow Spider Bite? (Definition/Background Information)

  • The black widow spider (genus Latrodectus) is a medium-sized (about an inch long) venomous spider that is well-known and feared. It is one of the few spider types that can break through the human skin. The black widow spider is found all over the world
  • Humans are generally bitten by the female black widow spider (which may be 1.5 inches in size), mainly when they are disturbed or while protecting their eggs. The spiders are active at night and may be found in dark corners and nooks. However, they are usually not found in places where humans live or reside
  • A physical examination of the affected area by a trained physician is usually sufficient to diagnose a Black Widow Spider Bite. Intense pain at the bite site may be felt, which is also the most common symptom
  • Black Widow Spider Bites are generally treated using anti-venom; but self-care measures, such as cold compresses and pain-relievers, can provide early relief
  • The prognosis is generally good with effective and immediate treatment; most individuals recover within 24 hours of treatment
  • Contrary to popular belief, a majority of individuals bitten by the black widow spider do not have significant health damage. Furthermore, typically a Black Widow Spider Bite does not cause death

Who gets Black Widow Spider Bite? (Age and Sex Distribution)

  • Any individual exposed to the black widow spider is vulnerable to be bitten; Black Widow Spider Bites are often defensive bites, when the spider is threatened
  • Children and elderly adults are generally affected more severely than young adults
  • The black widow spider is found all over the world in regions such as America, Australia, Asia, and Africa

What are the Risk Factors for Black Widow Spider Bite? (Predisposing Factors)

Risk factors associated with Black Widow Spider Bites include being in the endemic regions and:

  • Being in a woody and/or dark area
  • Not wearing protective clothing in high risk areas
  • Living in areas where these spiders are common is a potential risk factor

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider. 

What are the Causes of Black Widow Spider Bite? (Etiology)

  • Black Widow Spider Bites release a poisonous protein (neurotoxin) into the human skin which can affect the nervous system
  • The female black widow spider can inject a potentially dangerous toxin into the body that can cause the signs and symptoms associated with the bite

What are the Signs and Symptoms of Black Widow Spider Bite?

Black Widow Spider Bites causes a poisonous substance to be injected into the human body. The symptoms caused may differ from one individual to another; it may be severe in some, but mild in others. Usually the signs and symptoms last 3-7 days after the bite; occasionally, it may last up to a month.

Some of the common signs and symptoms include:

  • Sharp pain at the bite site
  • Severe muscle cramps
  • General weakness
  • Abdomen, shoulder, back, or chest pain
  • Tremors
  • Nausea and vomiting
  • Fainting, dizziness

How is Black Widow Spider Bite Diagnosed?

Black Widow Spider Bites may be diagnosed as follows:

  • A physical examination of the affected site by the physician is normally sufficient to diagnose the condition
  • In addition, the symptoms exhibited by the individual may be carefully observed
  • The individual may be asked to provide an account (history) of the events that occurred (what took place and how) 

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis. 

What are the possible Complications of Black Widow Spider Bite?

Typically, Black Widow Spider Bites do not cause any major complications. Rarely though, complications may arise that include:

  • Severe muscle cramps that can lead to kidney failure
  • Diaphoresis
  • Severe nausea and vomiting can lead to dehydration
  • Breathing difficulties
  • Increase in blood pressure: This can cause complications such as heart attacks and strokes
  • Increase in heart rate
  • Seizures             

How is Black Widow Spider Bite Treated?

The treatment measures for Black Widow Spider Bite may include:

  • Medical assistance should be sought without any delay
  • In the meantime, self-care remedies may be availed that include:
    • Remaining calm and not panicking
    • Washing the spider bite site with soap and water
    • It is not recommended to apply a tourniquet, since the harm caused by the compression of the tourniquet may be significantly more than its benefits    
    • Use of cold compresses on the bite site
    • Hot baths
    • Application of topical antibiotic creams
    • Use of over-the-counter pain-relievers, such as acetaminophen and ibuprofen, if necessary

Medications used in the treatment of Black Widow Spider Bites may include:

  • Narcotic pain relievers, if there is severe pain
  • Muscle relaxants to help with muscle cramps
  • Anti-venom formed from horse serum is seen to be effective, when there is severe pain refractory to the above measures, there is a risk of life-threatening complications, and to decrease the need for hospitalization

How can Black Widow Spider Bite be Prevented?

  • Wearing protective clothing in wooded areas, specifically in areas where black widow spiders are common, can help prevent bites
  • Use of pest control in areas where the spiders are found in large numbers can be useful

What is the Prognosis of Black Widow Spider Bite? (Outcomes/Resolutions)

  • The prognosis of Black Widow Spider Bite is generally good with effective and immediate treatment; relief may be obtained within 24 hours
  • In general, complications are not known to occur in healthy adults
  • When anti-venom is not used in the treatment of Black Widow Spider Bites, the symptoms may last for a few weeks. Also, the condition is only rarely fatal

Additional and Relevant Useful Information for Black Widow Spider Bite:

When antivenin is used to treat Black Widow Spider Bite, follow-up appointment is essential in order to watch for serum sickness (the body’s reaction to the horse serum).

What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 30, 2015
Last updated: March 18, 2018