Spider Bite

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How Dangerous Are Spider Bites?

Most spider bites are harmless. In fact, people usually don’t even notice when they’ve been bitten. Spider bite symptoms can be so subtle and non-specific—a red, inflamed bump that may be itchy—that it is often difficult to determine whether the person was bitten by a spider or not. However, the bites of some spiders, including the black widow and brown recluse, can cause serious complications and, in rare cases, be fatal.

Types of Spider Bites

A brown recluse bite may seem asymptomatic at first. However, the affected area usually becomes sore within 8 hours, and in some cases, the center of the bite swells, darkens, blisters and turns into an open sore over a week or so. Other symptoms of a brown recluse spider bite include nausea, fever, chills and rash. Read more about brown recluse spider bites below.

For health purposes, spider bites can be classified into two primary categories: poisonous spider bites and non-poisonous spider bites.

The vast majority of spiders in the United States are not poisonous. The bites of these spiders are harmless, although they can trigger an allergic reaction or become infected.

The two poisonous spiders that live in the United States are the black widow spider and brown recluse spider. Black widow spider bites tend to cause pain and cramping that usually start near the bite and spread throughout the body. Other black widow spider bite symptoms include nausea, vomiting, severe abdominal cramping, chills, fever and headache. Read more about black widow spider bites below.

What Spider Bites Look and Feel Like

Non-poisonous and poisonous spider bites can differ by how they appear and the symptoms they cause soon after and in the days following the bite.
Non-Poisonous Spider Bites

Most spider bites look similar to what you would expect from a mosquito bite: a red, swollen bump on your skin that may be itchy or painful. Because the large majority of spiders in the United States are not poisonous, most spider bites do not produce any additional symptoms.

However, poisonous spiders like the black widow and brown recluse can cause more severe symptoms with their bites.

Close-up of black widow bite fang marks on unseen man's finger
Photo Credit: David~O via Flickr
David~O via Flickr

Black Widow Spider Bites

Black widow spider bites can continue to swell, and you may even see small fang marks. Severe black widow bite reactions tend to be in the form of muscle cramps or intense pain that spreads, versus changes to the bite itself. Other black widow spider bite symptoms include:

Rarely, the black widow spider venom can cause a paralysis of the diaphragm that makes breathing difficult. Read more about black widow spider bites.

Brown Recluse Spider Bites

Brown recluse spider bites usually appear mild at first and will heal within a week. In more severe cases, pain around the bite develops within 3 to 8 hours. In rare cases, the bite wound turns dark (blue or purple) and forms an ulcer that eats away the surrounding skin. This is known as a necrotic wound, in which tissue becomes damaged or dies as the venom from the bite spreads. Other symptoms of a brown recluse spider bite include nausea, fever, chills and rash.

Doctors treat severe brown recluse spider bites with antibiotics to prevent or fight infection, and in some cases may recommend surgery to remove dead tissue. The wound will heal, but may leave scarring. Read more about brown recluse spider bites.

Spider Bite Treatment at Home

Most spider bites will heal without treatment. To prevent infection and increase comfort, you can:

  • Wash the affected area with soap and water for 20 seconds.
  • Apply an ice pack or cool compress to decrease swelling and ease pain.
  • Do not apply a tourniquet, which can cause more harm than good.
  • Consider over-the-counter (OTC) medication. If pain is interfering with activity or sleep, you can take acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) as directed on the packaging. An OTC antihistamine, such as diphenhydramine (Benadryl), can decrease itching.
  • Watch for any new symptoms that develop later, or for any signs of allergic reaction, such as swelling that spreads, fever, or difficulty breathing.

When to See a Doctor for a Spider Bite

Occasionally, an infection will develop at the site of a spider bite. If the bite looks worse rather than better in the days after the bite, or you notice pus and increased swelling, call your healthcare provider.

Go immediately to the nearest emergency room if you suspect the bite is due to a black widow or brown recluse spider. (Black widow spiders are found throughout the United States and feature an orange-red hourglass on their underbellies. Brown recluse spiders typically hide in dark, quiet places like wood piles and attics.) The bites of black widow and brown recluse spiders can be so serious that it’s important to get immediate medical attention, even if the affected person seems fine.

An allergic reaction to a spider bite is another reason to seek medical care. Minor swelling at the site of a bite isn’t cause for the concern, but if the swelling seems to be spreading, it is time to call a doctor. Call 911 if the affected person is having trouble breathing.

Who to See for a Spider Bite

Your primary care provider can handle most allergic reactions and infected spider bites. Emergency department personnel are best equipped to handle poisonous spider bites and severe allergic reactions (anaphylaxis) to spider bites.

Most spider bites won’t cause any serious health problems. However, it’s important to pay attention to symptoms and seek medical care as needed. When in doubt, consult your doctor.

Children and Toddler Spider Bites

If you know or suspect your child was bitten by a black widow or brown recluse, seek immediate medical care (call 911). Children, especially those with weakened immune systems, are at higher risk for a systemic reaction to the venom, which can cause serious complications or, rarely, death.

Because most spiders are non-poisonous, spider bites on children and toddlers typically heal with proper first aid and at-home treatment. However, young children may be more vulnerable to complications from poisonous spider bites like those from a black widow or brown recluse.

If your child appears to have a spider bite that you don’t suspect is venomous, follow these treatment steps:

  • Wash the affected area with soap and water for 20 seconds.
  • Cover the bite with a cloth and apply an ice pack, or place a cool, wet cloth on the bite.
  • Administer over-the-counter pain medication, such as children’s acetaminophen (Tylenol or store brand), if your child complains of pain around the bite.
  • Apply an antibiotic lotion or ointment to the bite to prevent infection.
  • Do not apply a tourniquet, which may cause more harm than good.
  • Monitor your child for any signs of allergic reaction, such as swelling that spreads beyond the bite or involves swelling of the lips or tongue.
  • Call 911 if your child has any difficulty breathing.

Brown Recluse Spider Bites

Brown recluse spiders are found in the Midwest and south central United States. They’re often identified by a dark violin-shaped mark on their backs, inspiring the nickname “fiddleback” spiders. They can live indoors or outdoors, typically within wood piles, sheds, or debris. Despite their dangerous reputation, brown recluse spiders are not innately aggressive, and brown recluse bites are rare.

What to Do for a Brown Recluse Spider Bite

If you know for certain or believe you have been bitten by a brown recluse, the first step is to remain calm and still. Moving too much could increase the flow of venom into your bloodstream.

To administer first aid for a brown recluse spider bite, follow these steps:

  • Wash the affected area with soap and water.
  • Cover the bite with a cloth and apply an ice pack, or place a cool, wet cloth on the bite.
  • Do not apply a tourniquet, which may cause more harm than good.
  • Monitor yourself or the victim for any signs of allergic reaction, such as swelling that spreads beyond the bite.
  • Call 911 if you or the victim has difficulty breathing.
  • For non-emergency bites, call poison control at 1-800-222-1222 to report the bite and get further instruction.
  • See your doctor or go to urgent care anytime you suspect a brown recluse spider bite.
  • If possible, catch the spider so doctors can confirm the type and administer the correct treatment.

Stages of a Brown Recluse Spider Bite

A brown recluse bite may seem asymptomatic at first. You may not even know you were bitten. However, the affected area usually becomes red and sore within 3 to 8 hours. You may also develop nausea, fever, chills and rash. For most people, this is the extent of the injury and the bite heals on its own within three weeks.

In more serious cases, the center of the bite swells, darkens, blisters and turns into an open sore over a week or so. The lesion may become necrotic, meaning the venom begins to destroy tissue. The wound may continue to grow over days, weeks or even months, resulting in a deep scar.

How Doctors Treat Brown Recluse Spider Bites

There is no antivenom or antidote for brown recluse spider bites; instead, treatment focuses on managing symptoms and preventing infection. Treatments for brown recluse spider bites include:

  • Antibiotics, which can be oral or intravenous (IV) to treat or prevent bacterial infection
  • Antihistamines, to reduce swelling and relieve itching
  • Surgery known as debridement, to remove dead, damaged or infected tissue and allow healthy tissue to grow

Are Brown Recluse Spider Bites Deadly?

Most brown recluse spider bites will heal without complications. It’s very rare for the body to have a systemic response to a brown recluse spider bite, in which the toxicity of the venom spreads beyond the initial wound and can become fatal. When this abnormal response does occur, it is typically in children or people with weakened immune systems.

In the past, many reported cases of severe brown recluse spider bites were misdiagnosed, and the wound was actually the result of a staph infection or other bacterial condition. As doctors have become more familiar with these types of infections, fewer actual cases of brown recluse spider bites have been reported. In fact, statistics show your odds of being struck by lightning are significantly higher than the likelihood of dying from a brown recluse spider bite.

How to Prevent Brown Recluse Spider Bites

Brown recluse spiders are called that for a reason—they prefer to steer clear of humans in spots like wood piles, garage corners, stacks of debris, or gardening boots and gloves. Many bites occur when someone inadvertently disturbs a brown recluse spider when moving items or putting on shoes or clothing where a spider may be hiding.

Take these steps to protect yourself from a potential brown recluse spider bite:

  • Shake out clothing, including gloves, jackets, shirts, boots or shoes, before putting them on—particularly if they’ve been stored in an attic, basement or garage.
  • Make noise or stomp your feet to cause vibrations before you enter a dark, quiet space, such as a basement, attic, closet or shed. This can startle the spiders and cause them to retreat.
  • Wear gloves when working with stored items, such as when cleaning out a garage, picking up wood piles, or grabbing items that have been in storage.
  • Keep your home clear of clutter, particularly in unused corners or rooms.
  • Lay down glue traps in rooms you don’t use often.
  • Call a professional pest control service if you are concerned about an infestation of brown recluse spiders in an area of your home.

Black Widow Spider Bites

The black widow spider is so steeped in myth and mystique that it’s inspired the name of a comic book superhero. However, the fictional crimefighter may be more dangerous, as black widow spider bites on humans are actually quite rare. Black widow spiders are not naturally aggressive and bite only in self-defense.

That said, the venom of a black widow spider—known for its distinctive red hourglass marking on the underside of females—is reported to be 15 times stronger than that of rattlesnake. This can cause serious complications or, rarely, death in young children, the elderly, or people with weakened immune systems. However, most symptoms from a black widow spider bite, while painful, are treatable and temporary.

What to Do for a Black Widow Spider Bite

If you know for certain or believe you have been bitten by a black widow, the first step is to remain calm. Too much movement could increase the flow of venom into your bloodstream.

To administer first aid for a black widow spider bite, follow these steps:

  • Seek immediate medical treatment. Call your doctor, urgent care, hospital, or poison control (1-800-222-1222) to report the bite and get further instruction.
  • Wash the affected area with soap and water.
  • Apply ice or a cold pack to the area of the bite.
  • Monitor yourself or the victim for any signs of allergic reaction, such as swelling that spreads beyond the bite. Swelling may be noticeable on the face, including mouth, lips and tongue.
  • Call 911 if you or the victim has difficulty breathing.
  • If possible, catch the spider so doctors can confirm the type and administer the correct treatment.

Stages of a Black Widow Spider Bite

Black widow spider bites tend to cause pain right away. You may also notice redness and swelling near the bite, and might even see one or two small fang marks. In many cases, this is the extent of the injury and the bite will heal without treatment.

For more severe bites, you may develop severe pain and muscle cramps within two hours. These cramps usually start near the bite, then spread through the body and intensify over the next 6 to 12 hours. In some cases, the pain is so severe people may believe they have appendicitis or a similar emergency condition. Other severe black widow spider bite symptoms include nausea, vomiting, severe abdominal cramping, chills, sweating, fever and headache.

Rarely, a black widow spider bite can cause a form of paralysis that affects the diaphragm, making breathing difficult. Do not try to diagnose the severity of breathing. Call 911 for any breathing symptoms.

How Doctors Treat Black Widow Spider Bites

There is an antivenom for black widow spiders available in the United States, Mexico and Canada. Doctors will typically administer antivenom if you are having problems breathing, have high blood pressure, or are pregnant.

For other patients with black widow spider bites, treatment includes:

  • Medications to reduce high blood pressure
  • Muscle relaxants, for muscle cramps
  • Narcotic medications, including benzodiazepines and opioids, for severe pain
  • Over-the-counter pain medication, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), for mild pain

Are Black Widow Spider Bites Deadly?

Black widow spider bites are more common than those from a brown recluse spider—2,500 black widow spider bites are reported in the U.S. each year—but the symptoms are usually treated effectively with antivenom and other medications. In world medical literature, there are only three recorded cases of fatal black widow spider bites, and in the United States, there are no known cases of death from a black widow spider bite.

The only recorded death related to a black widow spider bite was the result of a systemic reaction to the antivenom; however, the antivenom is usually administered safely and provides immediate, effective pain relief.

How to Prevent Black Widow Spider Bites

Black widow spiders like to hide in dark, protected areas, including garage corners, wood sheds, empty flower pots, boots, and piles of debris. Many bites occur when someone accidentally disturbs a black widow spider when moving items or putting on shoes or clothing where a spider may be hiding.

Take these steps to protect yourself from a potential black widow spider bite:

  • Always wear gloves when working with stored items, such as when cleaning out a garage, picking up wood piles, or grabbing items that have been in storage.
  • Shake out clothing, including gloves, jackets, shirts, boots or shoes, before putting them on—particularly if they’ve been stored in an attic, basement or garage.
  • Wear a hat when working outdoors in a dark, hidden area, such as under a porch or deck, or when working inside an attic, basement, garage or shed.
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Aug 13
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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