Almost every spider you find in your house is harmless. Out of the thousands of spider species in North America, only two groups pose a real medical risk: black widows and brown recluses. A few others, like yellow sac spiders, can deliver a painful bite but nothing life-threatening. Fewer than three people die from spider bites per year in the United States, so the actual danger is extremely low.
One quick note on language: spiders are technically venomous, not poisonous. Venomous means a creature injects toxin through a bite or sting. Poisonous means something is toxic when you eat or touch it. You could safely eat a black widow (though no one’s recommending it). But since most people search “poisonous,” we’ll cover exactly what you’re looking for.
Black Widow Spiders
Black widows are the most medically significant spiders you might encounter indoors. They’re glossy black with a distinctive red pattern on the underside of the abdomen, often described as an hourglass shape. They prefer dark, undisturbed spaces: garages, basements, crawl spaces, closets, and the undersides of furniture or shelving. They build messy, irregular webs close to the ground.
Their venom is a neurotoxin, meaning it affects the nervous system rather than destroying tissue at the bite site. Pain starts at the bite and can spread to the chest, abdomen, or entire body. Other symptoms include muscle cramping, sweating, fever, chills, nausea, difficulty breathing, headache, and high blood pressure. Most healthy adults recover fully, but bites can be dangerous for young children, elderly people, or anyone with compromised health. If you suspect a black widow bite, get medical attention quickly.
Brown Recluse Spiders
Brown recluses are the other spider worth genuine concern. They’re light to medium brown with a dark violin-shaped marking on the front section of the body, with the “neck” of the violin pointing toward the back. They have six eyes arranged in three pairs, unlike the eight eyes most spiders have.
Geography matters a lot here. Brown recluses live in a limited range across the south-central and southeastern United States, roughly from Texas to Georgia and up through the Midwest. According to researchers at the University of California, Riverside, if you don’t live in their established range, it is highly unlikely you have a brown recluse in your home. They are consistently misidentified. Many brown spiders with vaguely similar markings get blamed, but true recluses outside their native territory are rare.
Their venom destroys tissue around the bite, potentially causing a necrotic wound that ulcerates and takes weeks to heal. Not every bite leads to serious damage, though. Some produce only mild redness. The severity depends on how much venom was injected and individual reaction.
Yellow Sac Spiders
Yellow sac spiders are small, pale yellow or light green, and they build silk “sacs” in upper corners of rooms, along ceilings, or behind picture frames. They probably account for more spider bites than any other type of spider, largely because they’re common indoors and active at night, sometimes crawling across beds or getting trapped in clothing.
The bite is painful right away, with a burning sensation lasting up to an hour. Redness, swelling, and blistering can develop over the next one to ten hours. A small area of tissue damage occasionally forms at the bite site, but it’s far less serious than what a brown recluse causes and usually heals without scarring. Yellow sac bites are unpleasant but not medically dangerous for most people.
Spiders That Look Scary but Aren’t
The majority of spiders in your home are completely harmless, even the ones that look intimidating. Cellar spiders (sometimes called “daddy longlegs spiders”) are the pale, impossibly long-legged spiders that hang upside down in basements and corners. They’re fragile and their fangs can’t meaningfully penetrate human skin.
Wolf spiders are large, dark brown, fast-moving, and look aggressive. They don’t build webs. Instead, they actively chase prey across floors and walls. Despite their appearance, they’re basically harmless. They can bite if pinched or trapped, but the result is minor pain and swelling, similar to a bee sting. Wolf spiders are usually “accidental invaders” that wandered inside and don’t establish indoor populations. Females carry their egg sacs on their bodies and their babies ride on their backs after hatching, which can be startling but isn’t a sign of an infestation.
Jumping spiders are small, compact, often colorful, and have two oversized front-facing eyes that give them the best vision of any spider. They stalk and pounce on prey. They occasionally wander indoors and may spend the winter in a house. They’re curious and seem to “look at” you, but they pose zero risk.
Many “Spider Bites” Aren’t Spider Bites
Here’s something most people don’t realize: a large percentage of skin lesions blamed on spiders are actually bacterial infections. MRSA, a type of antibiotic-resistant staph infection, frequently gets misdiagnosed as a spider bite by both patients and healthcare workers. The wound looks similar: a red, swollen, painful area that may blister or develop a central ulcer. But unless you actually saw a spider bite you, the cause is more likely to be a skin infection, an ingrown hair, or a reaction to another insect entirely.
This matters because treating a staph infection requires antibiotics, while waiting for a “spider bite” to heal on its own can let the infection worsen. If you develop a painful, spreading skin wound and didn’t witness a spider biting you, consider that the cause might not be a spider at all.
What to Do if You’re Bitten
For any spider bite, clean the area with mild soap and water and apply a cool, damp cloth for about 15 minutes each hour to reduce swelling. Keeping the affected area elevated helps, and over-the-counter pain relievers can manage discomfort. An antihistamine can help with itching.
Seek medical care if you experience severe pain, stomach cramping, difficulty breathing or swallowing, or if the inflamed area keeps spreading or develops streaks. These are signs of a systemic reaction, most commonly associated with black widow venom, or a sign that a wound is becoming seriously infected regardless of the cause.