Spider bites can sometimes look like other types of skin lesions or bites from insects. Photos of spider bites can help you tell if you were bitten by a spider, but signs, symptoms, and appearance can overlap with other causes.

This article provides photos of different types of skin lesions and discusses whether or not they could be from a spider bite. This, however, can’t help you reach a concrete diagnosis.

The good news is that though more than 50 spiders in the United States have venom, their bites are not serious and usually only cause redness, swelling, and pain. Only two are venomous to humans: the black widow and the brown recluse.

Unless you actually catch a spider in the act, the only true way to tell if you were bitten by a spider is to be evaluated by a healthcare professional.

What Dangerous Spider Bites Look Like

Though it is possible to have a reaction to bites from any type of spider, most of the time, a non-venomous spider bite will not cause major problems. Black widow and brown recluse bites are more serious.

What Does a Brown Recluse Spider Bite Look Like?

A brown recluse spider bite may initially look red. Over time, the bite may develop into a blister. If untreated, it can become ulcerated, which means it will turn into a painful open sore. In some cases, cell death (necrosis) and scarring may occur over a period of time.

What Does a Black Widow Spider Bite Look Like?

A black widow spider bite may look less obvious than a brown recluse bite. You may feel a pinprick sensation when the spider bites you. You may be able to see two fang marks when looking closely at the bite. There may be redness and swelling at the site. 

Black widow venom can also cause whole-body symptoms. The venom works quickly, with these symptoms often appearing within an hour of being bitten.

Symptoms of a black widow bite include:

  • Muscle cramps or spasmsSweatingHeadacheSevere pain in the chest, back, or abdomenChills, fever, or nausea (with or without vomiting)

If you suspect that you’ve been bitten by a black widow spider, seek medical help right away.

Signs of a Possible Spider Bite

The following are signs that you may have been bitten by a spider.

Expanding Lesions

There are many different things that can cause a lesion that grows, expands, or spreads—including a bite from a spider. Though this type of lesion is common in brown recluse bites, it may also be a sign of another skin infection, such as impetigo.

If you are unsure whether the lesion is growing, draw a line around it. This will help you keep track of whether or not the rash or area of swelling is expanding. Be sure to note the time and date when a line is drawn so you can tell how fast the lesion expands.

Bullseye Rash

A bullseye rash—known as erythema migrans—can be a sign of a bite from a spider.

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

Bullseye rashes are most common in tick bites that result in Lyme disease, but can also be present with spider bites.

Fang Marks

Depending on the size and type of the spider that bites you, you may be able to see fang marks, or two small, side-by-side holes. Fang marks are sometimes seen with black widow bites.

Necrosis

Brown recluse spider bites can cause blisters that can, in turn, develop into ulcers. The venom in the bite can cause necrosis, or tissue death, around the bite site.

Signs That It May Not Be a Spider Bite

The first priority is not necessarily ruling out that you were bitten by a spider, but if you were bitten by a venomous spider.

Bullseye rashes, necrosis, expanding lesions, or fang marks at the wound site could be from a spider bite, including venomous ones like the black widows or brown recluse. Get medical attention so you can get a proper diagnosis and treatment.

NOT RECLUSE is an acronym for the signs that a wound or lesion is not caused by a brown recluse bite.

It stands for:

  • Numerous bitesOccurrenceTimingRed centerElevatedChronicLargeUlcerates too earlySwollenExudes moisture

The presence of any of these is an indicator that the wound isn’t from a brown recluse. The presence of two or more of these signs almost guarantees that it’s not.

Some of these are also signs that you are not likely dealing with a black widow bite or a bite from any spider altogether, for that matter.

Numerous Bites

In cases where there are multiple bites, they could be from insects that travel in groups, such as mosquitoes, bedbugs, or chiggers.

Multiple bites are not typically from spiders, especially not a brown recluse or black widow.

Occurrence

If you have a rash or bite after working outdoors, it’s possible that poison ivy, another type of insect, or a non-venomous spider could be the cause.

Brown recluse and black widow spiders prefer cool, dark places and are more likely to be found in an attic, barn, or wood pile.

Timing

Most spiders are more numerous from late summer into fall, during mating season. When outdoors in the winter, they go into a dormant state.

Brown recluse and black widow spiders, however, are most active between April and October, when the weather is warmer and drier. Brown recluses are notoriously inactive during the rest of the year.

Red Center

Though some spider bites can cause a small, red bump or redness in the area of the bite, a lesion with a red, inflamed center is not an indicator of a venomous spider bite.

A skin infection is more likely. In fact, a lesion that is swollen, warm to the touch, or red at the center area could be a staph infection.

Elevated

If your bite is a raised bump, it may be from a spider, but not a brown recluse. Brown recluse venom causes lesions that have dark, flat centers.

Chronic

If it takes a really long time for the lesion to heal, it might not be a brown recluse bite. They’ve got a reputation for lasting a while, but most brown recluse bites heal within three weeks, and the biggest of them heal within three months.

Large

Brown recluse bites are known for having dead tissue in the center of the lesion. However, the necrosis is not going to be bigger than 10 centimeters across (four inches).

A lot of infected sores are identified—even diagnosed—as spider bites. In truth, unless you have a spider to identify as the cause, the odds are against a spider bite.

Ulceration

Venom from the brown recluse spider can cause breaks in the skin that worsen and spread. But this process, known as ulceration, is a slow one that can take multiple weeks.

If you have a bite that ulcerates within a week, it’s probably not from a brown recluse.

Swelling

Brown recluse bites typically only cause significant swelling if the bite is on the head or feet. If you have a bite between the neck and ankles that swells, it is not likely to be from a venomous spider.

If you have extreme swelling from a bite on your face, see a doctor prompty.

Exudes Moisture

Though some spider bites cause blisters, brown recluse bites are known for being dry in the center. If it’s oozing pus or moisture, it’s very unlikely to be a brown recluse bite.

Any bug bite can lead to swelling from an allergic reaction or envenomation.

When to Call a Doctor

Though not all insect or spider bites will require a doctor’s attention right away, there are some situations where you should seek treatment.

A skin lesion that is ulcerated, oozing moisture, taking a long time to heal, or causing swelling on the hands, feet, or face could be from an allergic reaction or a skin infection that requires treatment.

Get medical attention if:

  • You show signs of an allergic reaction, such as whole-body itching, hives that spread, or swelling of the throatYou believe that you’ve been bitten by a venomous insect, like a black widow spiderYou develop a bullseye rash (this could be a sign of Lyme disease)

Even if these don’t apply, but your skin lesion grows or continues to get worse over a 24-hour period, you should see the doctor.

If not, it’s probably fine just to keep it clean and watch to see if it changes.

How Spider Bites Are Treated

In most cases, a spider bite can be successfully treated at home. A bite from any spider should be immediately washed with mild soap and water. Apply an antibiotic ointment three times a day. You can also take an over-the-counter nonsteroidal anti-inflammatory drug (NSAID), such as Advil (ibuprofen), if needed. If the bite itches, try taking an antihistamine such as Benadryl (diphenhydramine). 

Any bite that worsens over time or becomes infected should be evaluated by a healthcare provider. Black widow and brown recluse bites can be especially dangerous to small children. If you think your child may have been bitten by one of these spiders, seek emergency care at once.

If a black widow bite becomes very painful, your healthcare provider may treat it with muscle relaxants or stronger pain medications such as opioid analgesics. In severe cases, an antivenom can be given. Healthcare providers generally give antivenom as a last resort since it can cause an anaphylactic reaction in some people.

Brown recluse bites may take time to heal. They may also worsen over the first few days before they start to improve.

If a brown recluse bite grows in size and becomes painful, your healthcare provider may prescribe antibiotics. This will help keep the bite from becoming infected. In some cases, your healthcare provider may also recommend a tetanus shot.

Summary

Regardless of what caused your bite, it’s important to monitor the injury and watch for signs of infection or other complications. If you believe you are having an allergic reaction, contact your doctor right away.

A Word From Verywell

If you witness the bite, it can be helpful to capture the insect in a jar or box so that it can be identified—or to try to take a photo. This will help your doctor determine whether or not special treatment may be needed.

Frequently Asked Questions

  • What are the symptoms of a serious spider bite?
  • In North America, black widow and brown recluse bites are most likely to cause serious symptoms.With a black widow bite, you might feel pain immediately, and then have difficulty breathing, swollen eyes, headache, excess saliva, nausea, cramps, sweating, and rash.Brown recluse spider bites don’t hurt immediately but can cause a bull’s eye bruise and blisters with itchiness.
  • Are wolf spider bites dangerous?
  • Only if you happen to be allergic to the wolf spider’s venom, and most people are not. Wolf spider bites are typically about as bad as a bee sting, causing redness and pain that should go away in within 24 hours.
  • When should I get emergency help for a spider bite?
  • Call 911 immediately for the following signs:Trouble breathing or wheezingPerson has fainted or is too weak to standCall a doctor for advice if the bite seems to be spreading or if the person looks very sick or has a fever.

In North America, black widow and brown recluse bites are most likely to cause serious symptoms.

Only if you happen to be allergic to the wolf spider’s venom, and most people are not. Wolf spider bites are typically about as bad as a bee sting, causing redness and pain that should go away in within 24 hours.

Call 911 immediately for the following signs: