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

A spider 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 puts 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, in nearly all spiders, their venom 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.

However, 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 as venomous in the U.S. — black widow spiders and brown recluse spiders.

This article will look at 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.

a spider about to bite. Share on Pinterest
Spider bites are often hard to diagnose.

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 the doctor.

General symptoms of a spider bite may be:

  • swelling around the bite
  • itching or a rash
  • pain radiating from the bite
  • muscle pain or cramping
  • skin blisters that turn reddish purple
  • headache
  • nausea and vomiting
  • fever, chills, and sweating
  • difficulty breathing
  • increased blood pressure
  • anxiety or restlessness

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

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

If someone knows or believes a venomous spider has bitten them, they should see a doctor immediately if they experience any of the following:

  • severe pain
  • abdominal cramping
  • breathing problems

If someone is unsure if the spider that bit them is hazardous, they should contact their doctor to be sure. 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 redness
  • 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 corners, such as rock piles, woodpiles, and closets. It lives in the Midwest and southern States.

It is brown with a violin shaped pattern on its back.

A 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.
  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 (necrosis) may occur in some cases.

Other symptoms include:

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

Children may have a more severe reaction throughout the body, including:

  • weakness
  • fever
  • joint pain
  • hemolytic anemia, where blood cells die faster than the body makes them
  • low platelet levels in the blood
  • organ failure
  • blood clots throughout the body
  • seizures

A bite from a brown recluse spider can be fatal.

Treatment options may include:

  • antibiotics to prevent an infection
  • 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 chance that tissue damage will occur.

Learn more here about the brown recluse spider.

Black widow

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The black widow is shiny and black with a red hourglass shaped mark on the underside. It can be one-quarter to half-an-inch long.

It lives in the southern states of the U.S. It likes to hide in attics, woodpiles, fallen leaves, and in other debris. A black widow will make a web between two objects. If a person touches the web, the spider may bite.

The female is more dangerous than the male, as it has larger venomous glands.

When a black widow bites, the person will feel pain, and two fang marks may appear.

After the bite, symptoms may include:

  • pain and a burning sensation around the bite
  • redness and swelling around the bite
  • muscle pain and cramping may start within an hour
  • high blood pressure
  • rapid heart rate and breathing

Some people may experience:

  • muscle rigidity
  • nausea and vomiting
  • sweating
  • pain in the trunk or abdomen
  • pain spreading from the bite to other parts of the body, for example, down the leg

Anyone with a black widow bite should try to stay calm and seek prompt treatment.

It is worth noting that, in a study of over 23,409 people who experienced a black widow bite, 65% had minor symptoms, while 33.5% had moderate symptoms that needed treatment. Only 1.4% had life threatening effects.

However, without medical attention, a bite can sometimes be life threatening.

Find out more about black widow spider bites here.

Brazilian wandering spider

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The Brazilian wandering spider does not occur in the U.S. but in Central and South America. It uses venom instead of a web to catch and kill its prey.

Immediate symptoms include intense pain, swelling, and sweating in the area of the bite.

A person who is bitten by a Brazilian wandering spider may also have:

  • a rapid heart rate
  • high blood pressure
  • agitation
  • vomiting
  • drooling

In children, symptoms may include:

In males, the venom can cause a long lasting, painful erection, known as priapism.

Antivenin is available for treating the bite of a Brazilian wandering spider. The sooner the person receives this treatment, the better their chance of recovery.

Hobo spiders, tarantula, and wolf spiders

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Tarantula spider.

Other spiders that have a reputation for being dangerous are the hobo spider and the tarantula.

The hobo spider is a brown spider that people may confuse with a brown recluse. The tarantula is a large, hairy spider.

A bite from a hobo spider is not considered poisonous but may cause skin irritation for a day or so.

The wolf spider can be up to 2 inches across. It can bite, but the impact is usually like that of a small insect bite.

A tarantula bite in the U.S. usually only causes mild symptoms. The bite will feel like a bee sting. However, some species in other parts of the world can cause sickness and possibly death.

The bite may not have a severe impact, but when a tarantula feels stressed, it can also launch a wave of irritating hairs that can pierce the skin or eyes like fiberglass.

People can use sticky tape to remove the fibers from the skin, but hairs in the eyes may need medical attention.

Treating a spider bite

If a spider bites a person, they should:

  • Clean the area with water and mild soap to reduce the chances of infection.
  • Raise the affected body part above the level of the heart to reduce swelling.
  • Avoid physical activity, as this can make the venom spread more rapidly through the body.

It is a good idea to contact a doctor if:

  • A person believes a brown recluse or black widow spider has bitten them.
  • Symptoms are severe, persist, or worsen.
  • There are signs of infection or neurological symptoms.
  • There are changes in heartbeat, blood pressure, or breathing.

If possible, taking note of what the spider looks like may help a doctor understand the nature of the bite and decide on the best treatment.

Home remedies for spider bites

Symptoms from nondangerous spider bites usually go away on their own, but some home remedies can help reduce discomfort.

Here are a few tips on what to do if you get bitten:

  • Avoid scratching the wound.
  • Apply ice to the area.
  • Use over-the-counter antihistamines to relieve itching.
  • If necessary, use anti-inflammatory medicines, such as ibuprofen, to relieve pain.
  • If blisters develop, ask a healthcare provider about antibiotic ointment.

However, if there is more than a red lump, this could indicate a venomous spider bite. If symptoms other than a red lump in the bite area occur, the person should see a doctor.

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Wearing pants when hiking may help prevent spider bites.

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

Example 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.

Other things that look like a spider bite

Doctors often misdiagnose a spider bite. This may be because the person says it was a spider, but they do not know which type. Sometimes another condition can 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 see a doctor for a diagnosis.

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

Q:

I have seen some advice to capture the spider so a doctor can identify the bite. Is this a good idea?

A:

Yes, it will help the doctor determine if the spider is a venomous spider and what type, and this could affect the treatment plan. Catch the spider in a glass jar or take a picture of it.

Deborah Weatherspoon, PhD, RN, CRNA Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.