Black widow spiders get their name from an old belief that the female always kills and eats the male after mating, like a widow left behind after her “husband’s” death. The name stuck because the spiders are jet black and the females are dramatically larger than the males, sometimes outweighing them by more than 100 times. But the real story behind the name is more complicated, and more interesting, than the simple myth suggests.
The Name Comes From Mating Behavior
The “widow” part of the name refers to sexual cannibalism, where a female spider consumes the male during or after mating. Early observers noticed this happening and assumed it was standard behavior for the species. The “black” part is straightforward: the females are a distinctive glossy black. Put together, the image is vivid and memorable. A black spider that devours its mate and carries on alone.
The name applies to the entire genus Latrodectus, which was first described scientifically in 1805. By the 1930s, the full common name “black widow” was well established in American culture. The combination of a lethal-sounding reputation, a menacing appearance, and genuinely potent venom made the name impossible to shake.
How Often Females Actually Eat Males
Here’s where the myth diverges sharply from reality. In North American black widow species, the female killing the male is the exception, not the rule. According to the Burke Museum’s arachnology department, most male southern black widows (Latrodectus mactans) survive mating and go on to mate again. In the western black widow, the species found across most of the western United States, sexual cannibalism has never been documented in the wild.
Much of the misconception traces back to laboratory studies. When spiders mate in small cages, males have nowhere to escape after copulation. Under those artificial conditions, cannibalism rates skyrocket. One laboratory study recorded cannibalism in 92% of matings, compared to about 65% observed in nature for the same species. Even that 65% figure came from a Southern Hemisphere species where cannibalism is genuinely common. For the black widows most Americans encounter, the real number is far lower.
A study on western black widows found that well-fed females didn’t attack males at all. Among females in poor condition (and therefore hungrier), only 71% attempted an attack, and just 40% of those attempts were successful. So the actual cannibalism rate for hungry western black widows was roughly 28%, and for well-nourished ones, essentially zero.
Why Some Males Sacrifice Themselves
The story gets stranger in certain species. In the brown widow spider and the Australian redback spider (both close relatives), males actively participate in their own death. During mating, a male will somersault his body and position his abdomen directly in front of the female’s mouthparts, essentially offering himself as a meal.
This isn’t a glitch in the spider’s programming. Males that sacrifice themselves mate for longer and transfer more sperm, which means they father more offspring. The cannibalism also makes the female less receptive to mating with rival males afterward. For a tiny male who likely won’t survive long enough to find another mate anyway, this tradeoff can make evolutionary sense: die now and father more spiderlings, or escape and possibly never reproduce again. Research on brown widow males confirmed that they actively choose to mate with adult females despite the near-certain risk of being eaten, because the reproductive payoff is higher than mating with younger, safer females.
Even in these species, though, cannibalism rates top out around 40 to 60%, not the 100% the name implies.
Why the Name Stuck Anyway
The name “black widow” endures because it’s a perfect storm of storytelling. The spiders look the part. That glossy black body with the bright red hourglass marking is one of the most recognizable warning signs in the animal kingdom. Research published in Behavioral Ecology found that the red hourglass functions as a signal aimed primarily at birds and other vertebrate predators, not at insect prey. Wild birds were nearly three times less likely to attack a black widow model that had the red hourglass compared to an all-black model. The hourglass essentially screams “don’t eat me” to anything with color vision sharp enough to see it.
The combination of a genuinely dangerous venom, a warning-colored body, and a name that evokes murder made the black widow one of the most famous spiders on Earth. Scientists kept repeating the cannibalism claim in textbooks, often copying each other without checking field observations. By the time researchers began studying mating behavior in natural settings rather than laboratory cages, the name and the myth were too deeply embedded to correct in popular culture.
Other Widow Spiders Share the Name
The “widow” label extends beyond the classic black species. Brown widows, red widows, and several other Latrodectus species around the world all carry the widow name. There are at least 30 recognized species in the genus, found on every continent except Antarctica, and new species are still being described. The cannibalism rates and mating behaviors vary significantly across the group. Southern Hemisphere species like the Australian redback tend to show much higher rates of sexual cannibalism than their North American relatives, which helps explain why the myth holds up better for some species than others.
So the name “black widow” captures something real about these spiders, but it dramatically overstates how common the behavior actually is, at least for the species most people encounter. The females can and sometimes do eat the males. They just don’t do it nearly as often as the name, and a century of repetition, would have you believe.