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Spider bites are uncommon, but they can be painful and sometimes dangerous. However, very few spider species in the United States can harm humans.

Spiders will only bite in self-defense, for example, when they feel trapped or under threat. This could happen if a person puts their hand in a box where a spider is living or if they put on a jacket that has a spider hiding inside.

Most spiders use venom to kill their prey. In this sense, most spiders are venomous.

However, the venom in nearly all spiders is too weak to have a significant effect on a human. Also, the fangs of many species cannot pierce human skin. If a spider does bite, it will usually cause no more harm to a person than a moderate insect bite.

Yet, some species produce venom that is powerful enough to harm a person. The Centers for Disease Control and Prevention (CDC) list two types of spider in the U.S. as venomous — black widow spiders and brown recluse spiders.

This article will explain how to identify a spider bite, which species in the U.S. and nearby are dangerous, what to do if a venomous spider bites, and how to prevent bites.

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Brown recluse spider bite
Photography courtesy of Tannbreww4828/Wikimedia

Spider bites do not produce many distinctive features by which people can identify them.

They can look similar to many other bug bites. According to a 2011 study, they can also resemble a number of bacterial and other infections.

For this reason, a spider bite can be hard to diagnose, unless the person takes the spider that bit them to a doctor.

General symptoms of a spider bite include:

In people with light skin, the blisters will turn reddish purple. In people with dark skin tones, they may appear as a lumpy or bumpy cluster of lesions that is darker than the surrounding skin.

People who experience these symptoms should contact a doctor as soon as possible.

In time, a bite from a brown recluse spider can result in ulceration and tissue death, or necrosis. In rare cases, some types of spider bites can be life threatening.

If a person knows or suspects a venomous spider has bitten them, they should contact a doctor immediately if they experience any of the following:

If they are unsure whether the spider that bit them is hazardous, they should contact a healthcare professional to determine that. Proper diagnosis can lead to more effective treatment and shorter recovery time.

If possible, catch the spider or take a photo of it for identification.

Anaphylaxis

If a person has an allergy to spider venom, they may experience a severe reaction known as anaphylactic shock.

Symptoms of anaphylactic shock include:

  • severe itching, swelling, or change in skin color
  • rash or hives
  • difficulty breathing or a wheezing cough
  • stomach cramps
  • rapid swelling of the tongue, lips, eyes, or throat
  • loss of consciousness

Anyone who starts to experience any of these symptoms needs immediate medical attention.

People who know they have an allergy may carry an auto-injector with them. Anyone else who is nearby may need to help them use this device to deliver vital medication for their allergy.

The CDC consider two spiders to be dangerous in the U.S. These spiders are the brown recluse and the black widow.

Brown recluse

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The brown recluse spider likes to hide in dry, dark places, such as rock piles, woodpiles, and closets. It lives in the Midwest and the South. It is brown and has a violin-shaped pattern on its back.

The brown recluse can only bite under physical pressure, for example, if it is trapped against a person’s skin.

When they bite, the following may happen:

  1. The initial bite will be painless, but it will become increasingly painful over the next 2–8 hours.
  2. There may be two small puncture marks with swelling around them.
  3. A red ring may form around the pale center of the bite. In people with darker skin tones, this may appear as a raised ring with a flat center.
  4. A white blister usually forms, and a lesion or ulcer can develop. The ulcer will turn bluish violet, and the center will be hard and sunken. Some skin may slough.
  5. After this, the wound will usually heal, but this may take several weeks.
  6. Without treatment, tissue death may occur in some cases.

Other symptoms include:

  • headache
  • nausea
  • musculoskeletal pain
  • a general feeling of being unwell

Children may have a more severe reaction throughout the body, and they may experience:

A bite from a brown recluse spider can be fatal.

No specific antidote is available to treat a brown recluse spider bite, but the lesion will still need medical attention. Treatment options may include antibiotics to prevent an infection, or surgery to remove dead tissue.

The most severe effects of a brown recluse spider bite will not occur immediately. However, the sooner a person seeks help, the lower the risk that tissue damage will occur.

People who live in an area with potentially hazardous spiders should take precautions to avoid bites.

Examples of some precautions to take are:

  • Always zip up tents when camping and wear pants when hiking in areas where spiders are common.
  • Turn shoes upside down and tap them on the ground before putting them on.
  • Always check before reaching into boxes or in areas that are not regularly disturbed.
  • Keep basements and yards free of clutter.
  • Wear gloves when gardening or getting wood from the woodpile.

Learn more about the brown recluse spider here.

Black widow spider

Kimberly Hosey/Getty Images

The black widow spider has a reputation for giving a deadly bite. While the bite can be dangerous, especially for young people and older adults, it is not usually life threatening.

Black widow spiders like to hide in dark places, such as boots, gloves, woodpiles, and mulch. They do not chase after people, but they may bite if they feel they are under attack.

They are around the size of a half-dollar piece. They have a large rounded abdomen and appear black, shiny, and hard. They may carry a mark shaped like an hourglass, or spots or dots, and these can be red, orange, tan, or white. Their webs appear untidy.

Some people experience no symptoms after a bite from a black widow spider, but the following may happen:

  • Any pain will be immediate.
  • Tiny puncture wounds may be visible, and some swelling around the puncture site may develop.
  • Severe pain and muscle cramps may start within 2 hours.
  • These may spread from the area of the bite toward the center of the body.
  • In some cases, the pain may be severe, resembling that of appendicitis or a heart attack.
  • In rare cases, difficulty breathing may occur.

After receiving a bite, a person should wash the affected area with soap and water. If they have a severe reaction, they may need medical attention.

Someone should also call poison control at 1-800-222-1222 or use the Poison Control reporting tool.

Treatment options may include:

To prevent a bite from a black widow spider, people should:

  • shake out gloves, boots, and other items that they store in a shed or garage
  • wear gloves when working in the yard
  • wear a hat when working in a shed or under an outside porch

Doctors often misdiagnose a spider bite. This may be because a person says it was a spider, but they do not know which type. Also, another condition can sometimes resemble a spider bite.

Other causes include:

Most spiders will not bite a person, and very few are dangerous.

Some spiders like to rest in dark or sheltered places, such as shoes. If a person puts their foot or hand in a place where a spider is living, some spiders can bite.

People who live or spend time in areas where there are brown recluse or black widow spiders should know how to recognize them.

They should also check items such as boxes and boots for spiders if they have not used them for a while. Other forms of protection include wearing gloves when gardening or working around a wood or rock pile.

Anyone who has concerns about a bite or other skin symptoms should contact a doctor for diagnosis.

A range of products are available for purchase over the counter or online, including antihistamines, ibuprofen, and antibiotic ointment.

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