Black Widow Spider Bite

Medically Reviewed by Jabeen Begum, MD on June 21, 2024
Written by Shawna Seed
8 min read

The black widow is a medium-sized spider about a half-inch long. Three species are common to the United States:

The southern black widow. This spider has a shiny, black, globe-shaped belly (abdomen). You’ll know it by the red hourglass mark on the underside.

The northern black widow. You’ll notice a row of red spots down the middle of the upper surface of its abdomen. It also has two crosswise bars on the underside. Just to make things interesting, the markings can also be yellow or white. The spider may be brown or have red legs.

The western black widow. This spider is usually a glossy black, although it can appear to be brown or dark purple. It may have the red hourglass shape on its underside, but it might have two triangles separated by a space or a bar. The red color may be muted.

These spiders are active at night. They bite only when disturbed.

Male black widow spider

The male of this species has an elongated body with white and red markings on the sides. The male's legs are much longer in proportion to its body than are the female's. The male mates with a female in her web. After mating, the female often kills the male and eats him. Even if it escapes the female after mating, each male mates only once and then dies. Males don't bite.

Female black widow spider

Females rarely leave their webs. They stay close to protect their eggs. They usually try to escape from humans and their bites are a defensive tactic -- they're trying to protect their eggs. Their bites are toxic to humans. The lifespan of a female black widow spider is about 3 years. 

Where are black widows found?

Indoors, they prefer dark corners or crevices, like garages, crawl spaces, and basements. Outdoors, they're likely to be in woodpiles and hollow stumps, and under rocks. You also might find them in a dark, undisturbed place like a water meter box. Other hiding places include under furniture, inside boxes, and in drainage pipes. They've even been known to get inside shoes that are rarely worn. Northern black widows often make their webs in tree branches.

The black widow spider's web helps it trap things to eat. They'll eat other spiders -- including black widows -- and all kinds of insects. They're capable of killing things much larger than themselves,  such as cicadas and scorpions. If they can't find live prey, they'll eat dead insects. 

 

 

The black widow spider makes a venom that affects your nervous system. Some people are slightly affected by it, but others may have a serious response. The bite might leave two fang marks. 

Other symptoms include:

  • Muscles that begin to hurt and get stiff, usually within 8 hours
  • Nausea or vomiting
  • Trouble breathing
  • Serious belly pain or cramping
  • Heavy sweating
  • Rash and itching
  • Swollen eyelids
  • Weakness or shaking
  • Can't move your legs

If you have serious symptoms like these, seek medical help right away.

What does a bite from a black widow feel like?

You may not feel the initial bite, or it might feel like a pinprick. 

 

Whether you felt the bite or not, your symptoms may progress this way: 

Shortly after the bite. You may start to feel pain at the site of the bite. The area around it might swell and turn red. You might have a spot that looks like a target.

15 minutes to 1 hour after the bite. Pain may start to spread from the bite to other parts of your body. This will feel like a dull muscle ache. If you were bitten on the lower part of your body, you may have pain in your abdomen. If the spider bit the upper part of your body, you may notice the pain more in your chest. 

In the hours after the bite. You might start to have signs of a serious reaction to the bite, including muscle cramping, nausea, sweating, restlessness, and fever.

About 8 to 12 hours after the bite. The pain from the bite might start to ease. 

In the days after bite. You might continue to have other symptoms for a few days.

Many of the symptoms of a black widow bite can look like those of other conditions. But if you think you’ve been bitten by this spider, call your doctor or a poison control center right away. 

IMPORTANT: If you suspect your child was bitten by a black widow, get them to the emergency room. These bites can be fatal in young children as well as older people.

In the meantime, you can try these tips to ease your symptoms and prevent further infection:

  • Wash the area with soap and water.
  • Apply a cold washcloth or ice pack wrapped in cloth to the area.
  • Take an over-the-counter pain reliever like acetaminophen.
  • If the bite is on your arm or leg, elevate it to prevent swelling.
  • Apply an antibiotic cream or lotion to the bite.

If possible, capture and kill the spider (place it in a plastic bag or jar) and take it to your doctor visit. This way, they’ll know for sure whether it was a black widow that bit you.

The doctor will review your symptoms and decide what treatment, if any, you need. If your symptoms are serious, you may need muscle relaxants or stronger pain medicine. You might have to stay in the hospital, though that’s rarely the case.

In the most serious cases, the doctor may inject you with antivenin. It’s a drug made from substances in the blood of horses. Antivenin neutralizes the black widow’s venom. That means it prevents it from causing you harm.

Your doctor will use this treatment only after they've spoken with another doctor who has experience in treating these bites. Antivenin can cause a number of side effects, so if your doctor gives it to you, they’ll have to monitor you for about 8-12 days afterward.

Black widow spiders live in cool, dark places like sheds and garages. They normally bite only when they’re startled or surprised. You can take these steps to reduce your chances of a black widow spider bite:

Clean the house. Check areas around your house that might be attractive to spiders. You can vacuum up spiders, webs, and eggs.

Clear clutter. Cut down on boxes, junk piles, and anything else that might attract spiders in your garage or shed. 

Place traps. Use glue boards or sticky traps around windows, doors, vents, and other places spiders might enter. 

Check your shutters. If you have shutters, keep them clean. It's important to check behind them for spider webs.

Change your outdoor lights. Yellow bug lights or sodium vapor lights will attract fewer insects. Fewer insects means less food for spiders. 

Keep a clean perimeter. Keep woodpiles, building supplies, and other stacks of things away from the foundation of your house. When weather turns cold, spiders often try to migrate inside. 

Inspect clothing. If you have black widows nearby, shake out your clothes and shoes before you put them on. 

Use repellent. Spray your outdoor work clothes and shoes with an insect repellant such as DEET.

Dress appropriately. If you're doing any outside work that might bring you in contact with spiders, wear long sleeves, long pants, a hat, gloves, and boots. You may want to tape around your wrists so that spiders can't get inside your gloves. You also may want to tape your pant legs to your boots. 

 

 

False black widow spiders. The females are about the same size as black widows, but they don't have the red marking on the abdomen. They're common in the Southern and Western U.S. 

Brown widow spider. These spiders also are found in the Southern and Western U.S. They're tan rather than black. Brown widows can look a lot like immature black widows, which grow darker as they get older. Adult female brown widows are brown and often have an orange hourglass shape on their abdomen. At first glance, you might mistake that marking for the red hourglass seen on adult female black widows. 

Wolf spiders. These very common spiders are brown or gray. They might have stripes or other markings on their backs. They don't catch their food in webs -- they live underground and pounce on their prey. They're not aggressive toward people unless they feel threatened. They can be large -- as big as 2 inches across. They also are sometimes hairy. A wolf spider bite might turn red and swell, but it's not dangerous.

Brown recluse spiders. This species is tan or brown, and it has a marking on its back that looks like a violin. They're not aggressive and won't bite unless they feel threatened. A brown recluse bite can be painful, swollen, and red. Without treatment, you might develop an open wound that takes a long time to heal. These bites can be dangerous. 

Black widow spiders like dark, hidden places. You might find them inside living in boxes or under things. Outdoors, they might be in woodpiles or under rocks. Females have a distinctive red hourglass on their abdomens. They will bite to protect their eggs. You might not feel the bite at first, or it might feel like a pinprick. Within an hour or so, you may have pain, redness, and swelling around the bite. Pain might travel to your abdomen, back, or chest. You might sweat, have a fever, and become nauseated. Wash the wound with soap and water, and call a doctor if you have symptoms that spread beyond the site of the bite. 

How poisonous is a black widow spider?

Reactions to black widow bites can be mild or life-threatening. Children and older people are more at risk of serious complications. No deaths have been reported in the U.S. from black widow bites.

What happens if you get bitten by a black widow?

You might not feel much at first. Then the bite may turn red and swollen, and pain may start to spread away from the site of the bite. You might feel muscle aches in your abdomen, back, or chest. More serious symptoms include nausea, sweating, trouble breathing, and weak limbs.

How does black widow poison affect humans?

When a black widow bites you, it injects a neurotoxin that affects your nerves.