Are Black Widow Spiders Deadly?

Black Widow Spiders are found throughout the world. Their bites are rarely fatal, but the venom of widow spiders contains neurotoxins that could cause severe side effects in humans.

Jul 15, 2023By Lisa Szymanski
are black widow spiders deadly

The black widow spider is easily identified by its shiny black body and distinct red hourglass marking on the abdomen. True widows are found across the United States, South America, Africa, and West Indies. Black widow spiders are feared as the most dangerous spiders in the world owing to the potency of their neurotoxic venom.

However, these arachnids seldom cause fatal bites. To determine whether the black widow really is a deadly spider, this guide looks at ways to identify them, their preferred habitats, and the potency of their venom.

How to Identify a Black Widow Spider

male and female black widow spider
The black widow male and female in a web

The black widow spider (Latrodectus mactans) belongs to the Latrodectus genus of true widow spiders, of which there are 30 species. Black widows are known for their black color and red hourglass marking on the underside of the abdomen, but this is only true for females.

Female widow spiders reach a length of up to 2 inches compared to the much smaller males of less than 1 inch in size. Surprisingly, the male black widow spider does not have the hourglass marking on the abdomen or any other part of the body. Instead, the males of this poisonous species are lighter in color, with red and orange spots on their abdomens.

Where Do Black Widow Spiders Live?

black widow spider with egg
Black widows prefer rocks, wood piles, and shrubs

Lactrodectus spiders are found throughout the world, including the United States, Asia, Africa, Europe, Australia, and certain parts of South America. In fact, the only continent that widow spiders do not inhabit is Antarctica because they prefer warmer climates. The poisonous spiders live in grasslands, forests, and arid regions where they prefer to nest in wood piles and shrubs. But widow spiders in search of a dark and dry place to nest will make their way into surrounding homes where they encounter people.

They build dense webs in dark crevices and corners, making areas such as the basement, garage, or foundation ideal hiding spots. Their densely-woven webs are funnel shaped and mostly found near the ground.

Their Behavior

black widow spider prey
Catching her prey

The notorious widow spiders are not aggressive and will only bite if accidentally squashed or grabbed. Their name is derived from their cannibalistic behavior in which the females tend to eat their male counterparts after breeding. This behavior is mostly attributed to the Southern Hemisphere species. Latrodectus hatchlings, on the other hand, will eat their siblings soon after emerging from their eggs.

Widows build dense cobwebs to hide in during the day and will usually retreat into their web funnel when they feel threatened. The males and females of this species only come together to breed, after which the female can lay up to 200 eggs. Black widows are nocturnal and will come out at night to capture prey such as small insects, vertebrates, and other arachnids. These spiders wrap their prey in silk once they become entangled in the web, then paralyze them with one poisonous bite.

How Potent is Black Widow Spider Venom?

black widow spider venom
A single bite from a black widow takes down its prey

The Black Widow spider has earned its reputation as being one of the deadliest spiders in the world because of its highly neurotoxic venom. Interestingly, only the female black widow spider delivers a toxic bite that is more potent than rattlesnake venom! But owing to the small size of these arachnids, they deliver much less poison than rattlesnakes. A bite from this arachnid feels like a minor pinprick progressing to full-body pain and swelling within 12 hours.

Their venom contains latrotoxins that attack nerve cells with symptoms including profuse sweating, hypertension, nausea, and intense abdominal and back pain that lasts for 2-7 days. More severe symptoms involve respiratory paralysis making it hard to breathe.

Black Widow Spider Bites

black widow spider bite
Black Widow ready to strike

Black widow spiders don’t always envenomate their victims when they bite, which is known as a dry bite. While widows carry strong venom, only the females have fangs that are large enough to pierce human skin. A case study involving 23409 black widow venom exposures found that only 1.4% of victims presented with life-threatening symptoms. A black widow bite is very rarely fatal and only poses a possible risk to children and the elderly who don’t have strong immune systems.

If you are bitten by a black widow spider, it is best to wash the area with warm soapy water. Seek medical attention if symptoms such as pain and nausea worsen, or shortness of breath occurs.


black widow spider hourglass

Black widow spiders are highly venomous, and their bites are extremely painful. Although bites from these spiders can be medically significant, it is rarely fatal. Latrodectus spiders prefer to hide and will only bite when they feel threatened. These arachnids remain inside their burrows and feed on prey such as grasshoppers, mosquitoes, and other insects.

When spotting a black widow spider in the garden, don’t try to remove them and risk being bitten. Rather leave these shy arachnids to play their part in establishing a healthy ecosystem.

Lisa Szymanski
By Lisa Szymanski

Lisa is a wildlife enthusiast who enjoys hiking and gardening and has four years of experience volunteering at pet shelters. She is the proud mom of two dogs, a Pitbull named Ragnar, a Boerboel named Blueberry, and four feisty chickens, or as she calls them, the "queens of the yard," Goldie, Gray, Peaches, and Brownie.