Updated on January 2, 2025.
Spider bites are very common, and most don’t require medical treatment. There are more than 3,500 species of spider in the United States and only a handful have fangs that can penetrate human skin. Most of these have venom that isn’t dangerous to humans. If they bite, you may experience some discoloration, soreness, or a bit of swelling.
But not all spiders are harmless. In fact, tens of thousands of people visit the emergency room each year to get care for symptoms caused by suspected spider bites. And though they occasionally cause illness, they’re very rarely fatal. In the U.S., about three people die from spider bites each year, mostly children.
Here’s what to know about spider bites, what symptoms they cause, and how to treat and prevent them.
Why we need spiders
If you find spiders frightening, remember this: Most are harmless. In fact, they're necessary for the environment.
“Spiders are very much a part of our ecosystem," says digital health director and advisor Jon Pangia, DO, of Grand Strand Medical Center in Myrtle Beach, South Carolina.
Spiders are predators that prey on a diet of insects. This means most spiders are only dangerous if you’re a bug. In fact, around the world, spiders kill between 400 and 800 million metric tons of prey each year. This helps prevent pests from destroying crops.
"They're killing some of the other bugs, and they're keeping your yard cleaner than you ever could," says Dr. Pangia. What’s more, "Hardly any of them ever would even come close to biting you."
Why do spiders bite?
Spiders are not interested in sucking blood, like mosquitoes. Plus, they almost never bite people while they’re asleep, contrary to popular belief.
In fact, most spiders are not aggressive. They’re definitely not looking for a fight with a human many times its size. If they bite, they’re doing so out of self-defense. When a spider finds itself in danger of being crushed or caught, it may bite to save its life.
Recognizing a spider bite
Unless you see a spider bite you, which is rare, you probably won't notice a bite until after the fact, says Pangia. In most cases, a spider bite is similar to a mosquito bite—a discolored, itchy, or painful swollen spot that goes away on its own. These include bites from common spiders like the garden spider, jumping spider, woodlouse spider, nursery web spiders, cobweb spiders, sac spiders, and, very occasionally, wolf spiders.
Often, people mistake other types of bites for spider bites. These include bites from bloodsucking insects like lice, bedbugs, fleas, a variety of flies, or kissing bugs, which are mostly found in the southern regions of the U.S.
Other times, wounds that seem like spider bites are actually small bacterial infections, like cellulitis or methicillin-resistant staphylococcus aureus (MRSA). If you have a wound that isn’t healing, gets worse, drains pus, and/or causes a fever, seek medical treatment.
In the U.S., bites from two types of venomous spiders, the black widow and the brown recluse, can cause more serious reactions. These spiders tend to live in the midwestern, southern, and western regions of the country.
Watch for these signs of a black widow bite:
- Swelling, redness, and pain around the bite
- Double fang marks
- Muscle pain in chest, belly, shoulders, and back
- Anxiety
- Headache
- Nausea or vomiting
- Sweating
- Excess salivation (spit) and tears
- Eyelid swelling
- Weakness, tremors, or even paralysis, usually in the legs
Watch for these signs of a brown recluse bite:
- Burning, itching, or redness at the bite site that shows up after several hours or days
- Purple coloring around the bite area, surrounded by a white ring and a red ring, and resembling a bull’s-eye
- A blister or ulcer that turns black
- Headache or body aches
- Rash
- Fever
- Nausea or vomiting
Treatment for spider bites
If you have a spider bite and you saw the spider that bit you, treat the symptoms according to whether it was a brown recluse, black widow, or another type of spider. If you didn’t see the type of spider that bit you, then it’s important to keep an eye on your symptoms. If there is simply pain, redness, itchiness, and swelling, it’s not likely to be a serious bite.
“If it’s a small bite that’s not getting bigger, you can just leave it be, and it will probably go away,” says Pangia. If the bite is bothering you, you can take a few steps to help ease the pain or itch:
- Wash the area with soap and water.
- To reduce swelling, place ice or an ice pack wrapped in a cloth over the area, and keep the area elevated above the heart if possible.
- Take over-the-counter pain medication if needed.
- Apply an antibiotic cream to protect against infection.
For severe symptoms
Go to the emergency room if your symptoms become worse, or if you know you were bitten by a black widow or brown recluse. Even if the bite isn't poisonous, you could be having an allergic reaction, which can lead to swelling around the face and mouth, difficulty breathing, and trouble swallowing. Watch especially for severe symptoms in small children and older adults, whose immune symptoms may be weaker.
If you’re unsure what type of bite it is or whether it requires a trip to see a healthcare provider, call 911 or Poison Control at 1-800-222-1222 right away and they can provide instructions.
Spider bite prevention
The first step toward prevention is learning what venomous spiders look like and where they typically live. If you live in a woodsy area, you know that it’s impossible to keep spiders out of your yard. But you can take measures to protect yourself while you are outdoors:
- Use insect repellent registered with the U.S. Environmental Protection Agency (EPA).
- Treat your outdoor clothing and boots with permethrin, an insecticide.
- Wear long-sleeved shirts and pants when spending time in the woods, or in garages or sheds.
- Wear gloves whenever you’re working outdoors or moving wood or rocks.
- Shake out work gloves, hats, and boots before putting them on.
To keep spiders out of your home:
- Keep the areas around the house’s foundation cleared.
- Trim trees and bushes so they don’t touch the house.
- Clean and vacuum regularly.
- Be sure to stop up any open drafts and keep doors and windows shut tight.
“They can get into the tiniest of holes,” says Pangia. Pay special attention during the fall months, he adds. “They're trying to find a warm place to spend the winter, so that's when you really have to be extra vigilant."
With a little care and attentiveness, humans and spiders can live together in peace.
