Spider Bites: Signs, Symptoms, and When to Seek Treatment (With Pictures)

The thought of a spider bite and the harm it could cause can be scary. Although there are thousands of species of spiders in the world, only a handful of spiders are poisonous to humans. Almost all spiders make some type of venom. But spider bites often aren’t dangerous because their fangs are either too short or delicate to break the skin, or their venom doesn’t affect people. Fortunately, very few poisonous spiders are found in North America. 

Even though there are few poisonous spiders, their bites have to be taken seriously. Left untreated, spider bites can become infected or cause serious tissue damage. Very rarely, a spider bite could be deadly. Let’s take a closer look at spider bites and what to do if you’ve been bitten.

How do I know if I got bit by a spider?

Sometimes it’s really hard to know if you’ve been bitten by a spider — especially because signs of most spider bites aren’t very specific. Common spider bite signs to look for include:

• Sudden pain or itching

• Two small breaks in the skin or a small red bump

• Redness

• Swelling

• Target-shaped or bullseye spot on the skin

• Dark or discolored area on the skin

• Development of an ulcer in 3 to 4 days

• Development of muscle cramps, headache, and/or severe pain

Spider bite symptoms can sometimes look similar to injuries caused by other biting insects or other skin trauma. But if you see a spider on you, or if you’ve been in an environment where spiders like to hang out, this could be a sign that the mark on your skin could be a spider bite. Things that increase the likelihood you’ve been bitten by a spider include:

• Being in secluded, dark places (like attics, barns, or cellars)

• Being in tall grass or wood piles

• Putting on clothes or shoes without shaking them out first

What does a spider bite look like?

Spider bites don’t all look the same. And they can look different on different people. Spider bites may look different depending on:

• What type of spider caused the bite

• How long has passed since the bite took place

• How much venom was injected

• How strongly you react to the venom 

Here are some pictures to help you identify signs of different types of spider bites. 

A smooth, pink bump from a spider bite.

Two small blisters at the site of spider bite surrounded by redness and swelling.

A red rash surrounding a spider bite (also known as a bullseye rash).

A brown recluse spider bite with blisters surrounded by a large, dark red patch.

A spider bite causes a crusty and bloody skin wound surrounded by redness.

A skin wound (ulcer) caused by a spider bite.

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Which spiders are most likely to bite?

According to experts, spiders in the U.S. are not normally aggressive or venomous. But any spider can bite, especially if it’s being disturbed. Although rare, the most medically important spider bites are ones caused by brown recluse and black widow spiders. Although less severe, common bites also come from these spiders:

• Wolf spider

• Garden spider 

• Trapdoor spider

• Mouse spider

• Huntsman spider

• Running spider

• Green lynx spider

• False black widow spider

• Jumping spider

• Tarantula

• Orb spider

• Crab spider

• Parson spider

Keep in mind that if you are allergic to the venom, even a normally mild spider bite can be serious. In rare cases, they can cause severe allergic reactions, like anaphylaxis (more on this below).

What to do if you suspect you’ve been bitten by a spider

Most spider bites are harmless. But any break in the skin can lead to an infection. Following these simple steps will help control pain and reduce the risk of infection:

• Wash the area with soap and water right away.

• Place an ice pack on the area of the bite.

• Take an over-the-counter pain medication, if needed. Acetaminophen (Tylenol) or Ibuprofen (Motrin, Advil) are good options.

• Use an antihistamine like diphenhydramine (Benadryl) for swelling.

• Get medical attention for young children or adults with serious symptoms.

• Get a tetanus booster if your vaccines aren’t up to date.

How do I know if a spider bite is getting infected?

Despite your best efforts to clean the area, a spider bite could still get infected. Some of the signs of a spider bite infection include:

• Redness or swelling extending out from the bite

• Warmth in the area

• Pain

• Yellowish drainage (pus)

• Fever

Signs of an infected spider bite can overlap with signs of the bite itself. The thing to keep in mind is that most spider bites should get progressively better after a day or two. If the symptoms are getting worse, it could be a sign of infection or that a venomous spider caused the bite.

When to seek medical treatment for a spider bite

It’s important to take all spider bites seriously. Fortunately, you can treat most spider bites at home. But sometimes you may need to get medical treatment. Some things that should prompt you to seek medical treatment are:

• You recognize the spider as being poisonous (or if you suspect it is).

• You experience headache, abdominal cramping, or nausea and vomiting.

• You feel pain that continues to get worse or spreads elsewhere on your body.

• You see yellowish discharge (pus) drains from the area, or the bite becomes an open sore.

• You have fever, chills, joint pain, or body aches. 

• You feel pain, redness, or swelling that continues to get worse after 24 hours.

In rare cases, spider bites are a medical emergency. You should get immediate care if you have any of these signs of a severe allergic reaction:

• Rapid heart rate

• Trouble breathing or swallowing

• Chest tightness

• Swelling of your mouth or face

Images used with permission from VisualDx (www.visualdx.com)