How dangerous is a black widow spider bite?
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The bottom line
Black widow spider bites often are painful right away. After a bad bite, severe pain and muscle cramps can start in an hour or less. Pain and muscle cramps can be treated. An antivenom is available but is needed only rarely.
Prevention tips
Do not put your hands into places you cannot see.
Shake out your gardening gloves before putting them on. Shake out boots or shoes that you have stored in garages, basements, or sheds before putting them on.
Always wear gloves when moving wood, reaching into wood piles, handling mulch, and grabbing empty flowerpots.
If you are working in a garage or shed, or under a porch or deck, wear a hat to protect your head.
If you see black widow spiders around your home, contact a pest control service.
This really happened
A 3-year-old boy was riding his bike when he felt extreme ear pain and screamed for his father to remove his helmet. The ear was inflamed, and the boy was given ibuprofen and diphenhydramine for a suspected bee sting. Within a half hour, he was sweaty, complaining of abdominal pain, lying on the floor, and refusing to move from that position. EMS transported him to an emergency department. There, the boy was in obvious distress, and his abdomen was tender and rigid. He was given medication for pain. The father reported that the boy’s helmet had a spider web containing a dead moth in it. (The boy’s uncle later found a female black widow spider in the helmet.) Over the next 2–3 hours, the boy had progressive respiratory distress and agitation requiring sedative medication. The poison center recommended antivenom, but none was available at that hospital. The boy’s mental status and respiratory distress worsened. A breathing tube was inserted, and the boy was transferred by air ambulance to a hospital with a pediatric intensive care unit. At the PICU, antivenom was ordered, but the boy’s mother refused it because her sister had recently died from an anaphylactic reaction (the cause was not recorded). Approximately 12 hours after the bite, the boy pulled out the breathing tube. He had some continued pain and occasional agitation that required medication. He was discharged from the hospital after 3 days (from Friedman et al., 2021).
What does a black widow spider look like?
Female black widow spiders (Latrodectus mactans in the east and L. hesperus in the west) have bodies up to a half-inch in length plus long legs. They appear hard, black, and shiny. The abdominal section is large and rounded. Their classic marking is a red hourglass shape on the underside of the abdomen, but the marks can be orange or white or tan. Their webs look tangled and messy.
Female black widows have fangs and can inject venom into humans. The male spiders are rarely seen. They are very small and are often eaten by the females after mating — the source of the name black widow. Males have fangs, but they are too short to harm humans.
What to do if you are bitten by a black widow spider
If someone is bitten by a black widow spider, use the webPOISONCONTROL® online tool to get help, or call your poison center at 1-800-222-1222. Whether online or by phone, expert guidance is always free, confidential, and available 24 hours a day.
Where do black widow spiders live?
Black widow spiders are typically nocturnal and like dark, undisturbed areas. You might find them in stacks of wood, brush piles, outhouses, corners of garages and sheds, under flowerpots, inside gardening gloves and boots, and other sheltered places. Black widow spiders are not aggressive, but they will bite if they feel threatened.
Are black widow spider bites dangerous?
Death following a black widow spider bite is very rare. Most bites result in symptoms ranging from mild to moderate. In a review of over 15,000 black widow exposures reported to US poison centers, there were no deaths and only 10% resulted in hospital admission.
What are the symptoms of a black widow spider bite?
A black widow spider bite is usually painful right away. There can be visible puncture wounds at the bite site and local swelling and sweating. The pain from the bite spreads outward — pain from a bite on the hand will spread up the arm to the shoulder, chest, and abdomen. Black widow spider bites can cause muscle cramps in 15–60 minutes. These often start at the site of the bite and can progress to other areas, especially the back, chest, and abdomen.
The pain and muscle cramps can come in waves that leave the person writhing. Nausea, vomiting, sweating, and high blood pressure occur frequently. Recovery usually occurs within 24–48 hours, but symptoms can persist for several days.
How are black widow spider bites treated?
The first step in treating a black widow bite is to clean the bite area with soap and water. Oral pain relievers can be given. Anyone who is bitten needs protection from tetanus. If you haven't had a tetanus booster shot in the previous 5 years, call your physician or go to an urgent care center.
In the emergency department, opioid medications can be given for pain, and benzodiazepine drugs can be given to relieve anxiety and muscle spasms. There is an antivenom for black widow bites, but not all hospitals have it. While it is effective, the antivenom is made from horse serum, and some people can have dangerous allergic reactions (anaphylaxis) to it. A negative test for allergy to the product does not guarantee that a reaction will not occur. The antivenom is reserved for people whose symptoms cannot be controlled with other treatments.
When should you go to the ER for a black widow spider bite?
Evaluation in the emergency department is appropriate for people whose pain is not controlled by oral pain medication. In the review of 15,000 exposures, about half were managed at home.
References
Antivenin (Latrodectus mactans). Merck. Revised April 2023. Accessed July 10, 2026.
Antivenin shortage notice. ASHP. March 10, 2026.
Repplinger DJ, Hahn I-H. Black widow spider (Latrodectus mactans; hourglass spider). In: Nelson LS, Howland MA, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS (eds). Goldfrank’s Toxicological Emergencies. 11th ed. McGraw-Hill Education. 2019.