7 Facts About the Black Widow Spider

Black widows have a reputation that they don't (always) deserve. Sharon Keating/Shutterstock

Male black widow spiders do their best to avoid getting eaten, however.

Mention the black widow spider and you'll likely be greeted with a few frantic glances and exclamations of "What?! Where?!"

The black widow, however, isn't as dangerous or as one-dimensional a creature as popular culture suggests. It certainly has a venomous bite, but it also has an incredibly strong web and a decidedly odd courting ritual in which male spiders become homewreckers.

Black Widow Spiders Are More Than Just Black

Belonging to the genus Latrodectus, widow spiders encompass 31 known species that exist on every continent in the world save for Antarctica. While the three species common to North America — southern (L. mactans), western (L. hesperus) and northern (L. variolus) — are black, some are a light to dark brown, like the appropriately named brown widow spider (L. geometricus). Some of the species — but not all of them — have some kind of distinct red marking abdomen.

Female Black Widow Spiders' Venom Is Potent but Rarely Deadly

The venom of the black widow is decidedly potent, rated to be about 15 times stronger than that of a rattlesnake, but a bite from one doesn't mean death. The bite will bring on muscle pain along with a variety of other symptoms, including trouble breathing, nausea and numbness around the bite site. These symptoms can become severe, but unless you're a child or someone who's already ill or has a weakened immune system, they are rarely fatal. Only female black widows will poison a human since only their chelicerae — a hollow, needle-like mouth part — is long enough to inject the venom into humans. Additionally, black widow spiders are unlikely to bite you in low-threatening situations, and they may not even use their venom if they do bite you.

A female black widow spider sits near its egg sac while a male black widow spider approaches
Male black widow spiders, one of which is pictured above at right, have a variety of techniques for mating with females. Mark_Kostich/Shutterstock

Black Widow Spiders Don't Often Eat Their Mates

Black Widow Spiders Don't Often Eat Their Mates

Aside from their distinct appearance and their venomous bite, the thing female black widows spiders are best known for is killing their mates and devouring them after sex. This trait is so commonly applied to the species that the phrase black widow is used to refer to a human woman who has killed at least one partner or lover. This reputation for killing, however, is generally undeserved. Mate eating has never been recorded in the wild when it comes to most North American species, according to the Burke Museum; it has only being observed in lab settings where the male couldn't escape. This doesn't mean that it doesn't happen with other members of the genus, but it isn't the norm.

Male Black Widow Spiders Do Their Best to Avoid Getting Eaten

Despite the fact that sexual cannibalism is fairly rare among the black widows, males do try their best to not become a post-coital snack. A 2014 study published in Animal Behavior found that male black widows seek out well-fed virgins for mating. In both controlled field studies and in the wild, researchers observed that males prefer such females, telling them apart from other females due to pheromones they release. In addition to avoid getting devoured by hungry females, researchers believe the males think a fatter female will result in more and healthier offspring.

Male black widows will also send out vibrations on a female's web that indicates they are there for mating and are not food. According to a 2014 study published in Frontiers in Zoology, the web plucks done by males differ significantly from that of prey. When researchers played back these vibrations to females, they were less likely to provide a predatory response than when the researchers played back prey vibrations.

Male Black Widow Spiders Are Literal Homewreckers

As in much of the animal kingdom, competition for mating can be fierce, so males often resort to all kinds of tactics to ensure that their genes are the ones carried on. In the case of the western black widow, this apparently involves destroying a female's web. Black widows' webs are messy cobwebs unlike the orderly spider webs we often see, and when they're ready to mate, females deposit pheromones onto the webs. Males will destroy the web, reducing the females' pheromones and making the web less attractive to other males. For their part, females don't seem to mind the destruction of their property. Researchers believe this is because it cuts down on the potential harassment they experience during mating periods. Indeed, the web reduction even seems to make the females more receptive to mating.

The Webs of Black Widow Spiders Are Strong as Steel

This particular web is known for its strength, so much so that researchers have been doing their best to replicate the web's properties. Attempts to do so, however, have not yielded materials with the same strength or properties. A 2018 study published in the Proceedings of the National Academy of Sciences may have remedied this issue, however. Using state-of-the-art imaging techniques, researchers took a closer look than ever before at the protein gland where the web silk is created. There, they discovered a more complex protein assembly process. Being able to synthetically replicated this process could result in stronger materials for bridges, better materials for plastics and more durable fabrics for military personnel and athletes.

Black Widow Spiders Are Heading North

Another sign of the climate-change times, the range of the northern black widow is expanding to what used to be colder climates. Outlined in a 2018 PLOS One article, Canadian researchers, relying on citizen science data, found that the northernmost range of the species has increased by some 31 miles (50 kilometers) between 1960 and 2016, creeping into eastern Ontario and Quebec.