Discover Four Fascinating Facts About Black Widows

The venomous spiders are nimble, secretive and dangerous

A black widow spider hangs from its web.

They are not the world’s deadliest spider

Contrary to the Marvel comic’s claim, black widows are far from the deadliest spider on Earth. But they do have a more intimidating name than the world’s actual most-venomous spiders, Australia’s funnel-web spiders. The Australian redback spider, a close relative of American black widows, is another contender because its venom is more potent and its bites are more common than funnel-webs.

Black widows are the most venomous spider in North America. Their venom is about 15 times stronger than rattlesnake venom, and uses a chemical called alpha-latrotoxin to overwhelm nerve cells and cause immense pain. When the alpha-latrotoxin reaches a person’s nerve cell, the nerve dumps all of its signaling chemicals at once, overwhelming its neighbors. In addition to pain, the a bite can cause swelling around the wound, severe cramping, sweating and chills.

Antivenom exists for bite victims

Roughly 2,500 people go to poison control centers with black widow bites each year to shorten the symptoms with the help of antivenom. Antivenom isn’t prescribed in every case—usually just if the patient is at high risk, has trouble breathing, has high blood pressure or is pregnant.

Antivenom to black widow bites was first manufactured in the 1930s. To make the antivenom, pharmaceutical producers expose horses to small amounts of black widow venom. The horse’s immune system reacts by creating antibodies that target chemicals in the venom. Pharmaceutical producers draw blood with those antibodies and purify them to be used in victims. Those antibodies neutralize venom by flagging a person’s immune system to destroy the pain-inducing chemicals.

Not one, but many species exist

Three North American spider species go by the common name “black widow.” They are the western species, Latrodectus hesperus; the northern species, Latrodectus variolus; and the southern species, Latrodectus mactans. Female black widows can reach about one and a half inches long. They are shiny and black, with bright red hourglass-shaped markings on their abdomens. Males are half the size, lighter-colored and have red or pink spots.

As their names suggest, the southern black widow lives across the southern United States, the western along the west coast and in the desert, and the northern black widow can be found in the upper contiguous U.S. and southern Canada.

Black widows share their taxonomic genus with a wild array of 30 other spiders found around the world. The newest addition to the Latrodectus genus, the Phinda button spider, was discovered in 2019 in South Africa, and it lays bright purple eggs.

The young spiders are cannibals

Marvel’s “Black Widow” was trained to kill from a young age, and young black widow spiders have a penchant for violence, too. Research published in 2016 in the journal Animal Behavior showed that when black widow spiderlings hatch together at many different sizes, the largest among them quickly consume their smallest siblings. In trials when the spiderlings hatched at about the same size, they didn’t jump to cannibalism right away.

“The last thing a mother wants is out of her 300 babies, to have one giant one and 299 dead ones,” said spider expert Jonathan Pruitt of the University of California at Santa Barbara to the Washington Post’s Joshua Rapp Learn in 2016. “It really suggests that females have been able to provision their eggs very precisely… so their development is in lockstep.”