Spider Bites Overview

How to recognize dangerous and harmful spider bites—and what to do about them

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Almost all spiders have venom. Some bite people, but most spider bites are not dangerous. Of all the spiders in North America, only two can actually make you sick: the black widow and the brown recluse.

This article discusses various types of spiders found in the United States. It describes what signs to look for so you can tell if you've been bitten by a spider that might be dangerous.

You'll also learn how you can avoid certain spiders and prevent getting bitten.

Spider Bites

Verywell / Joshua Seong

General Spider Bite Symptoms

It's almost impossible to identify a spider bite based on its looks. That's because bites from all kinds of insects can cause the same symptoms, including:

  • Redness
  • Swelling
  • Itching
  • Pain

Signs that a bite is more serious include:

  • Redness spreading away from the bite
  • Drainage (pus) from the bite
  • Increased pain
  • Numbness or tingling
  • Discoloration around the bite that looks like a halo or a bullseye

Spider bite symptoms can differ depending on the type of spider involved (more on that below). They can start right away or take hours or longer to develop.

Importantly, serious spider bites can also be accompanied by other symptoms, such as abdominal cramps and breathing problems. These bites require immediate medical attention.

Dangerous Spider Bites

Only two spiders in North America are considered dangerous. These are the black widow and the brown recluse.

Here are ways to tell if your bite could be from one of these spiders.

Black Widow Spider Bites

In the United States, black widow spiders, females in particular, are considered the most dangerous. While males may be hard to distinguish from other spiders, females have a unique red/orange-colored hourglass shape on their underside.

Female black widow spider

Kimberly Hosey / Getty Images

Their venom contains a toxin (a poisonous substance) that can cause a body-wide (systemic) reaction, not just a reaction at the site of the bite itself.

This photo contains content that some people may find graphic or disturbing.

Black widow spider bite

DermNet / CC BY-NC-ND

Symptoms of a Black Widow Spider Bite

A black widow bite can potentially affect muscle and nerve function. However, most of the time the only signs are mild and include:

  • "Fang" marks (tiny twin holes): These are telltale signs that are only visible right after the bite happens, before any swelling or redness occurs.
  • Immediate sharp or moderate pain from the bite itself, followed by swelling and redness at the site 30 to 40 minutes later

When severe symptoms occur, they usually do so within 30 to 60 minutes.

These can include:

  • Sweating
  • Chills
  • Fever
  • Nausea or vomiting
  • Headache
  • Dizziness
  • Muscle cramps
  • Rapid pulse or very high blood pressure
  • Exhaustion
  • Stupor or restlessness
  • Shock
  • Severe pain in the abdomen, back or chest

Muscle cramps and spasms near the bite that spread and increase in severity over the course of six to 12 hours.


It is extremely rare for a black widow bite to be fatal. In 2018, there were 1,015 recorded cases of black widow spider bites in the U.S. Six patients had potentially life-threatening symptoms, but none of them died.

Brown Recluse Spider Bites

Brown recluse spiders are only found in the Southeast United States. They are often described as having a violin-shaped mark on the back of their midsections. But they don't always have this mark, and it can be very faint.

Given this, they are very difficult to identify—even for trained spider experts.

Brown recluse spider

Schiz-Art / Getty Images

Even though a wound left behind by a brown recluse can look pretty serious, brown recluse spiders are much less likely to cause significant injury than black widows.

Symptoms of a Brown Recluse Spider Bite

You might not feel anything after a bite at first. Symptoms that can develop over time from a brown recluse bite include:

  • Reddened skin at the site of the bite that may turn into a blister (after four to eight hours)
  • Mild to intense pain and itching that lasts for two to eight hours after being bitten
  • An open sore (ulcer) that causes necrosis (tissue death). This tends to develop in a week or longer, and it can take months to heal.

In some cases, people can have a severe, systemic reaction to brown recluse spider bites. Signs and symptoms include:

  • Fever and chills
  • A rash all over the body that consists of tiny, flat purple and red spots on the skin
  • Nausea or vomiting
  • Joint pain

It's actually easier to figure out when a bite is not from a recluse than when it is. One way to rule out brown recluse bites is to see how your bite matches up with the following qualities. (The first letters of each conveniently spell NOT RECLUSE to make them easier to remember.)

  • Numerous: If there are more lesions than just one or two, they're not from a brown recluse. Brown recluse bites come in ones and sometimes twos.
  • Occurrence: Brown recluse bites usually happen when you disturb the spider. Most of the time these spiders hide in closets or attics, possibly inside boxes. Occasionally, the spider can find its way into a bed and bite a person while they are asleep. If the spider bit you while you were gardening or doing something outside, it's probably not a brown recluse bite.
  • Timing: If the bite didn't occur from April to October, it's very unlikely that it's a brown recluse bite.
  • Red center: Brown recluse bites are almost never red and inflamed in the center of the lesion. Usually, they're pale, blue, or purple. They can be red around the outside. But if it's red in the center, it's probably not a brown recluse bite.
  • Elevated: Brown recluse spider bites are flat or slightly sunken. If a lesion is raised up more than 1 cm above the normal skin surface, it's probably not a recluse bite.
  • Chronic: It takes around three months for a recluse spider bite to heal. If it takes more or less than that, it is unlikely to be a brown recluse bite.
  • Large: The largest areas of necrosis, or dying tissue, are smaller than 4 inches across. A recluse bite can be red and swollen well past that area, but there won't be dead tissue.
  • Ulcerates too early: Brown recluse bites take at least a week to break the skin and crust over. If it's crusty before seven days, it's probably not a brown recluse bite.
  • Swollen: Brown recluse bites are flat or sunken in the middle, not swollen. If it's swollen, especially if it's red, it's not a brown recluse. Bites on the face, especially the eyelids, are exceptions to this rule. Those swell a lot.
  • Exudes moisture: Brown recluse bites are dry, not moist. If it has pus oozing out of it, it's an infection rather than a spider bite.

Recap

The only two spiders in the United States that can be dangerous are the brown recluse and the black widow. However, it is very rare for someone to experience a life-threatening or fatal reaction from these spider bites.

Non-Dangerous Spider Bites

There are more than 40,000 species of spiders in the world, but most of them are too small, or their venom is too weak, to be dangerous to humans.

Here are some North American spiders that are often thought to be dangerous even though they are generally harmless:

  • Hobo spiders: These spiders were introduced into the Northwest United States from Europe in the 1980s. Since then, they've been blamed for instances of tissue death. A study published in the Journal of Medical Entomology in 2011 found no medical significance from hobo spider venom, however. 
  • Wolf spiders: Originally from Australia, wolf spiders are commonly thought to be very dangerous. But research on spider bites thought to be from wolf spider bites in the United States noted no cases of serious injury.
  • Yellow sac spiders: The bite of a common sac spider can be mistaken for a brown recluse bite, but the symptoms are not dangerous. These spiders are found throughout the United States.
  • Tarantulas: Bites from tarantulas can be painful, but they are not dangerous. However, when a tarantula is threatened, it can release a cloud of its hairs. The hairs can cause redness, itching, and swelling of the skin. Tarantulas inhabit states in the South and Southwest.
  • Brown widow spiders: The brown widow was discovered in areas of Southern California in 2003. It's venom is strong, but it injects such a small amount that it causes no harm beyond pain while being bitten and a small bite mark.
  • False black widows: False black widow spiders live in coastal regions of the Atlantic, Gulf, and Pacific states, as well as in Southern and Western states. Their bites can cause similar symptoms as true black widow bite, but they are much less severe.
  • Camel spiders: Camel spiders are technically not spiders or insects, but solifugids. They are found in desert regions. If they bite, they can cause a painful pinch, but they are not venomous or dangerous.
  • Jumping spiders: Jumping spiders are found from Canada and the Atlantic Coast states to California. They retreat from people when they are approached. If you handle them, they generally do not bite. If they do bite, you may experience minor pain, itching, swelling, and redness for a day or two.

Signs of Allergic Reaction

Though there are many spiders that are generally considered non-dangerous, it's important to know that any type of bug bite can cause anaphylaxis in some people. This is a life-threatening type of allergic reaction. The following signs warrant calling 911:

How Spider Bites Are Diagnosed

Determining whether or not you have a spider bite may be impossible unless you were able to catch the spider and show it to a spider expert.

This is especially true for the brown recluse spider. Skin infections and boils are often misdiagnosed as brown recluse spider bites.

It can also be hard to tell the difference between a spider bite reaction and a serious infection called community-acquired methicillin-resistant Staphylococcus aureus (MRSA).

MRSA is an antibiotic-resistant bacteria that can be found in lots of community settings, such as college dorms. If it's not treated, it can enter the bloodstream and cause life-threatening infections.

The main difference between MRSA and spider bites is that MRSA blisters contain pus and spider bites contain fluid.

Your healthcare provider will examine you, review your symptoms, and ask about the circumstances surrounding your suspected bite as they work to sort out your diagnosis.

Recap

Skin rashes and sores, like boils from infections, are frequently misdiagnosed as spider bites. This is because of similar symptoms and the fact that there are no means to test for the presence of spider venom.

How to Treat Spider Bites

Serious spider bite symptoms—whether you think they are from a dangerous spider or not—warrant an immediate medical evaluation.

But the good news is that most spider bites can be treated at home like any other bug bite. They usually heal on their own in about a week, unless the bite is from a brown recluse.

Here's what to do if you think you've been bitten:

  • Clean the wound with soap and water.
  • Apply an antibiotic ointment (like Neosporin) to help prevent infection.
  • Use a cool compress on the bite for no longer than 15 minutes at a time to reduce pain and swelling.
  • If the wound is on a limb, try to elevate it.
  • Take an over-the-counter pain reliever like Advil (ibuprofen) or Aleve (naproxen sodium) to relieve discomfort.

If you notice that the wound is getting worse or you develop any systemic symptoms like fever or chills, or are just feeling unwell overall, call your doctor. They may prescribe an oral antibiotic to treat an infection or consider other interventions, depending on your symptoms.

It's also a good idea to call a doctor if you are not up-to-date on your tetanus vaccination. Bites from insects or animals can sometimes transmit the bacteria that causes tetanus.

Preventing Spider Bites

Spiders only bite when they feel threatened. In other words, they do not seek out people to "attack."

The best way to avoid encountering brown recluse or black widows is to understand their habits.

Both of these types of spiders tend to prefer quiet, undisturbed areas such as closets, garages, basements, and attics. They may also congregate in stacks of firewood and other items next to the outside of houses.

Here are some tips for reducing your risk of encountering these spiders:

  • Reduce clutter in indoor areas where they may gather. Store items in plastic tubs rather than cardboard boxes, which are easier for spiders to get into and hide.
  • Keep firewood and other items in places where they do not make direct contact with the outside of your home. Shrubs, vines, and tree limbs touching the house should also be trimmed back since these give spiders shelter and a convenient bridge to your house. 
  • Install tight-fitting window screens and door sweeps to keep spiders from entering your home.
  • Clean your house routinely, using a vacuum in areas where spiders and their egg sacs may be.

Summary

Only two spiders in the United States are capable of causing serious bites. These are the black widow and the brown recluse spiders. Thankfully, dangerous or life-threatening reactions are rare.

While other spider bites may certainly not be without bothersome symptoms, they are not considered dangerous save for the fact that they—like any bug—can cause an allergic reaction in some people.

It's not uncommon for someone to think they have a spider bite when they really have a skin infection. If your bite is concerning, see a healthcare provider.

A Word From Verywell

If you live in an area of the country that is known to have brown recluse or black widow spiders, the best thing to do is to familiarize yourself with their habits and habitats so you can avoid them.

It is also a good idea to know what bites from these spiders do and don't look like, and review them with anyone you may live with.

Frequently Asked Questions

  • What do spider bites look like?

    Spider bites are red and swollen. More serious ones may have pus or discoloration, and black widow bites can have twin holes. However, many spider bites look like bites from other bugs, so they can be hard to identify.

  • How can you tell if you were bitten by a spider?

    It is very difficult to tell if you have actually been bitten by a spider unless you were able to catch the spider and show it to a spider expert or a doctor who knows how to identify spiders.

  • How do you treat spider bites?

    Clean the bite with soap and warm water, and apply a cold washcloth or ice pack. An over-the-counter antihistamine (for itching) or pain reliever (for discomfort and swelling) can also help. Seek immediate medical care if symptoms are severe or get worse.

  • What spider bites cause blisters?

    Brown recluse spider bites can cause a blister that's surrounded by either a bruise or reddish skin around the outside. A hobo spider bite can cause blisters with pus.

  • How long do spider bites last?

    For non-dangerous spider bites, the pain and swelling last about one to two days. A brown recluse spider bite usually heals within eight weeks. For black widow bites, your symptoms will typically get better in two days and disappear in five days, but you may notice mild symptoms for weeks.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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