Can a Black Widow Spider Kill You?

The female black widow is far more likely to bite a human than the male. Mark Kostich/Getty Images

Key Takeaways

Black widow spiders are known for their potent venom, which is up to 15 times stronger than a rattlesnake's, but bites are rarely fatal to humans.
These spiders prefer dark, dry places like wood piles, barns and basements, and are generally not aggressive unless disturbed.
Female black widows are distinguished by their shiny black bodies and red hourglass markings, and they are more likely to bite than males.

David Nelsen, an associate professor of biology at Southern Adventist University in Collegedale, Tennessee remembers sprawling on his belly under the slide at the elementary school playground, in search of the tangled web of the Latrodectus hesperus, aka the western black widow spider. He'd know it when he saw it, the sticky silk threads spun in messy snarls characteristic of such wondrous creatures. If he nudged the web with his long forceps in just the right place, he could catch the spider before it escaped and tuck it into one of his plastic bags where dozens of other black widows lay in wait.

It didn't matter that one bite from the shiny black spider could send his muscles into painful spasms within minutes; That even if he went to the emergency room writhing in pain, doctors likely wouldn't have the antivenom to treat him; That he'd have to wait out the burning, throbbing, and involuntary muscle contractions for hours or possibly days until his symptoms eventually subsided.

Nelsen wasn't concerned because he was getting to know these "sexy little organisms" rather intimately. They played a starring role in his doctoral research, and he wanted to understand them better.

So how did the black widow spider get its name, and why do people find them so scary?

Why It's Called a Black Widow

Nelsen chose the black widow for his research because "they're mysterious and dangerous," he says. Indeed, the black widow is one of the deadliest spiders in the world, according to Encyclopedia Britannica. About 2,600 black widow bites are reported to the U.S. National Poison Data System each year.

But its name comes not so much from the spider's ability to kill humans, but from a cannibalistic behavior noticed in the species during copulation. An entomologist collected samples of male and female black widows and stored them in the same container. When he came back to check on the spiders, he discovered that the female widows had eaten the males.

This so-called "spider cannibalism" is not that rare in the spider world in general, Nelsen says. It usually involves the female eating the male before, during or after copulation. But it is rarely seen in black widows that inhabit North America. Black widow males, in nature, tend to escape quickly after copulating — a luxury they weren't afforded caged together with females in a laboratory setting. Also, research shows that male black widows can sense chemicals in the female's web that indicate whether the she has recently eaten. They know to avoid hungry females, just in case.

Black Widow Spider Facts

This male black widow (*Latrodectus mactans*) was found under a rock in Pine Mountain Wilderness, Prescott National Forest, Arizona Tanthalas39/Wikimedia Commons/CC BY 3.0

Black widows build their tangled cobwebs in dark, dry places — wood piles, barns, greenhouses, basements, outhouses and latrines, hollow stumps, under lawn furniture and playground equipment, and in dense vegetation. They hide during the day in tiny crevasses or rodent holes, and creep out onto their webs during the night. When they do, they usually hang upside down waiting for a fly or grasshopper to get trapped in the sticky threads of their web.

When an insect gets caught, the widow quickly runs over and wraps it in silk. At mealtime, the spider digs its fangs into its prey, injecting the insect with digestive juices until it liquifies, and then the widow sucks up the resulting bug juice.

So how can you tell when you're face to face (so to speak) with a black widow spider? Here are the identifying characteristics:

Female black widow spiders are about 1.5 inches (3.8 centimeters) in length, with long legs. Males are about half that size.
Female black widow spiders have a shiny black body, with the well-known hourglass shape on their abdomens, in red, red-orange or yellow.
Males are lighter in color with red or pink spots. But color variations and markings vary depending on the species.
Black widow spiders are generally not aggressive. In fact, they will only bite a person if they're touched, trapped or sat upon.

There are 32 species of spiders in the Latrodectus genus, many of which are considered true widows. You can find black widows in every continent of the world except Antarctica. The western black widow (Latrodectus hesperus), southern black widow (Latrodectus mactans), and the northern black widow (Latrodectus variolus) are found mainly in the southern and western regions of the United States.

Black Widow Spider Bites

black widow defensive silk — The black widow spins a defensive silk that looks like a pearl necklace when its legs are touched. David Nelsen, Ph.D.

Black widows are not aggressive, Nelsen points out. They're shy, even. If you find one, there's no point in grabbing bug spray or swatting it dead. They won't come after you. In fact, they don't want to be around you as much as you don't want to be around them. Leave them be. Black widows play an important role in our ecosystem, feasting on many insect species, especially small, annoying insects like mosquitoes and flies.

Bites usually occur by accident, for instance, when you stick your hand in a gardening glove and startle one hiding there. Females are much more likely than males to envenomate (inject venom into) humans. The venom is pretty potent — up to 15 times stronger than a rattlesnake's, according to National Geographic. You could actually die from a black widow bite, but it's unlikely. One study looking at 23,409 cases of exposure to black widow venom found that only 1.4 percent of patients had life-threatening symptoms while 65 percent had minor symptoms. Young children, the elderly and people with compromised immunity are at greater risk of serious complications.

Black widow venom contains neurotoxins (toxins that act on the nervous system) called latrotoxins. If their tiny fangs do break your skin (it feels like a pinprick) and the venom does enter your bloodstream, you'll know pretty quickly. Within seconds, you'll feel pain and throbbing at the bite site. The area around your wound will begin to swell. As the venom travels through your bloodstream, the pain, swelling, and muscle contractions spread as well. If your diaphragm is affected, breathing becomes labored. Your heart can begin to race. You may become nauseous and sweat or have chills.

For minor bites, all you need to do is wash the affected area with soap and water and take an over-the-counter pain medication. But if you have serious symptoms, like the ones described above, seek medical attention. Doctors will treat your pain, and if they have the FDA-approved black widow antivenom, (availability is limited) you'll feel better within hours if it's administered quickly. But they may be hesitant to give it to you due to reports of severe allergic reactions and other ill effects. It's unlikely you'll be hospitalized, and even less likely you'll die.

Now That's Cool

Nelsen has found that if you pick at black widow spiders' webs, they'll bolt for cover. If they can't hide, they'll play dead. If you touch them and they can't escape, they'll dig their fangs into you. But if you pull gently on one of their legs with a pair of featherlight tweezers, they'll reach back into their spinneret and toss a sticky strand of silk your way. This defensive silk, which Nelsen describes as looking "just like a pearl necklace," sticks to predators, dries quickly, and can afford the widow extra time to get away. "I know of no other spiders that actively protect themselves with silk," Nelsen says. Other people have noticed this black widow behavior, he says, but no one has ever formally studied it.

Frequently Asked Questions

What should you do if you encounter a black widow spider?

If you encounter a black widow spider, avoid disturbing it. These spiders are not aggressive and will typically only bite in self-defense. If you're bitten, clean the area with soap and water and seek medical attention if severe symptoms develop.

How can you prevent black widow spiders from inhabiting your home?

To prevent black widow spiders from entering your home, seal cracks and gaps in doors and windows, remove debris and wood piles from around your house, and keep your living spaces clutter-free. Regular cleaning and reducing potential hiding spots can also help keep these spiders at bay.